U.S. patent application number 12/899448 was filed with the patent office on 2011-10-06 for method and apparatus for using channel state information reference signal in wireless communication system.
This patent application is currently assigned to QUALCOMM INCORPORATED. Invention is credited to Kapil Bhattad, Amir Farajidana, Alexei Yurievitch Gorokhov, Juan Montojo.
Application Number | 20110244877 12/899448 |
Document ID | / |
Family ID | 43706791 |
Filed Date | 2011-10-06 |
United States Patent
Application |
20110244877 |
Kind Code |
A1 |
Farajidana; Amir ; et
al. |
October 6, 2011 |
METHOD AND APPARATUS FOR USING CHANNEL STATE INFORMATION REFERENCE
SIGNAL IN WIRELESS COMMUNICATION SYSTEM
Abstract
A method for wireless communication is disclosed which includes
selecting a first resource pattern comprising resource elements
that are non-colocated with a second resource pattern and
allocating the first resource pattern to a plurality of antennas
for transmitting a channel state information reference signal.
Inventors: |
Farajidana; Amir;
(Sunnyvale, CA) ; Gorokhov; Alexei Yurievitch;
(San Diego, CA) ; Montojo; Juan; (San Diego,
CA) ; Bhattad; Kapil; (San Diego, CA) |
Assignee: |
QUALCOMM INCORPORATED
San Diego
CA
|
Family ID: |
43706791 |
Appl. No.: |
12/899448 |
Filed: |
October 6, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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61249906 |
Oct 8, 2009 |
|
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61257187 |
Nov 2, 2009 |
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Current U.S.
Class: |
455/452.2 ;
455/450 |
Current CPC
Class: |
H04L 5/0073 20130101;
H04L 5/0023 20130101; H04L 5/005 20130101; H04L 5/0051 20130101;
H04L 5/0035 20130101; H04L 5/0048 20130101; H04L 5/0053
20130101 |
Class at
Publication: |
455/452.2 ;
455/450 |
International
Class: |
H04W 72/08 20090101
H04W072/08; H04W 72/04 20090101 H04W072/04 |
Claims
1. A method for wireless communication, comprising: selecting a
first resource pattern comprising resource elements, the first
resource pattern being non-colocated with a second resource
pattern; and allocating the first resource pattern to a plurality
of antennas for transmitting a channel state information reference
signal (CSI-RS).
2. The method of claim 1, wherein the second resource pattern
comprises transmission resources allocated, in one or more cells,
to one or more of a user equipment reference signal, a common
reference signal and a control signal.
3. The method of claim 1, wherein the second resource pattern
comprises transmission resources allocated to one or more of a sync
signal, a paging signal and a broadcast signal.
4. The method of claim 1, further comprising limiting CSI-RS
transmissions from the plurality of antennas to a predetermined
number of subframes.
5. The method of claim 4, wherein the limiting further comprises
coordinating with at least one other cell so that CSI-RS
transmissions thereof are also limited to the predetermined number
of subframes.
6. The method of claim 1, further comprising selectively hopping
the first resource pattern.
7. The method of claim 6, wherein the selectively hopping the first
resource pattern comprises selectively hopping the first resource
pattern as a function of one or more of a subframe type and a cell
identification.
8. The method of claim 7, further comprising enabling or disabling
the selective hopping.
9. The method of claim 8, further comprising signaling the enabling
or disabling of the selective hopping to a user equipment.
10. The method of claim 6, further comprising signaling a hopping
schedule parameter to a user equipment.
11. The method of claim 1, wherein the second resource pattern
comprises a transmission resource pattern allocated in another
cell.
12. The method of claim 1, wherein the allocating the first
resource pattern comprises: grouping the first resource pattern in
a plurality of groups of resource elements; and assigning a group
of resource elements to an antenna of the plurality of
antennas.
13. The method of claim 12, wherein CSI-RS transmissions from the
plurality of antennas are orthogonal to each other in one or more
of a time domain, a frequency domain and a code domain.
14. The method of claim 12, wherein the grouping comprises grouping
two resource elements in a group.
15. The method of claim 1, wherein the allocating comprises
allocating a predetermined number of the uniformly spaced resource
elements to each antenna of the plurality of antennas.
16. The method of claim 1, wherein the second resource pattern
comprises transmission resources allocated to a common reference
signal in another cell.
17. The method of claim 1, wherein the selecting the first resource
pattern is based on one or more of a cell identification, a number
of the plurality of antennas and a subframe index for transmission
of the CSI-RS.
18. An apparatus for wireless communication, comprising: means for
selecting a first resource pattern comprising resource elements,
the first resource pattern being non-colocated with a second
resource pattern; and means for allocating the first resource
pattern to a plurality of antennas for transmitting a channel state
information reference signal (CSI-RS).
19. The apparatus of claim 18, further comprising means for
limiting CSI-RS transmissions from the plurality of antennas to a
predetermined number of subframes.
20. The apparatus of claim 18, further comprising means for
selectively hopping the first resource pattern.
21. An apparatus for wireless communication, comprising: a
processor configured for: selecting a first resource pattern
comprising resource elements, the first resource pattern being
non-colocated with a second resource pattern; and allocating the
first resource pattern to a plurality of antennas for transmitting
a channel state information reference signal (CSI-RS).
22. The apparatus of claim 21, wherein the processor is further
configured for allocating a predetermined number of the uniformly
spaced resource elements to each antenna of the plurality of
antennas.
23. A computer program product, comprising: a computer-readable
storage medium comprising: instructions for causing at least one
computer to select a first resource pattern comprising resource
elements, the first resource pattern being non-colocated with a
second resource pattern; and instructions for causing the at least
one computer to allocate the first resource pattern to a plurality
of antennas for transmitting a channel state information reference
signal (CSI-RS).
24. The computer program product of claim 23, wherein the
instructions for causing the at least one computer to allocate
further comprises instructions for causing the at least one
computer to: group the first resource pattern in a plurality of
groups of resource elements; and assign a group of resource
elements to an antenna of the plurality of antennas.
25. The computer program product of claim 23, wherein the
computer-readable storage medium further comprises instructions for
causing the at least one computer to limit CSI-RS transmissions
from the plurality of antennas to a predetermined number of
subframes.
26. A method for wireless communication, comprising: coordinating,
with a base station in a neighboring cell, a resource pattern
allocated for transmission of a reference signal; and muting, based
on the coordination, the resource pattern at locations
corresponding resource pattern allocated in the neighboring
cell.
27. The method of claim 26, further comprising orthogonalizing the
resource pattern with respect to the corresponding resource pattern
allocated in the neighboring cell.
28. The method of claim 26, further comprising signaling, to a user
equipment, information related to the muting.
29. The method of claim 26, wherein the coordinating comprises
coordinating the resource pattern allocated for transmission of a
channel state information reference signal.
30. An apparatus for wireless communication, comprising: means for
coordinating, with a base station of a neighboring cell, a resource
pattern allocated for transmission of a reference signal; and means
for muting, based on the coordination, the resource pattern at
locations corresponding resource pattern allocated in the
neighboring cell.
31. A method for wireless communication, comprising: receiving a
first resource pattern comprising resource elements that are
non-colocated with a second resource pattern; receiving a channel
state information reference signal (CSI-RS) according to the first
resource pattern; and performing a channel quality estimate based
on the CSI-RS.
32. The method of claim 31, further comprising receiving one of a
user equipment reference signal and a common reference signal
according to the second resource pattern.
33. The method of claim 31, further comprising reporting the
channel quality estimate to a base station.
34. An apparatus for wireless communication, comprising: means for
receiving a first resource pattern comprising resource elements
that are non-colocated with a second resource pattern; means for
receiving a channel state information reference signal (CSI-RS)
according to the first resource pattern; and means for performing a
channel quality estimate based on the CSI-RS.
35. The apparatus of claim 34, further comprising means for
receiving one of a user equipment reference signal and a common
reference signal according to the second resource pattern.
36. A computer program product, comprising: a computer-readable
storage medium comprising: instructions for causing at least one
computer to receive a first resource pattern comprising resource
element groups that are non-colocated with a second resource
pattern; instructions for causing the at least one computer to
receive a channel state information reference signal (CSI-RS)
according to the first resource pattern; and instructions for
causing the at least one computer to perform a channel quality
estimate based on the CSI-RS.
37. An apparatus for wireless communication, comprising: a
processor configured for: receiving a first resource pattern
comprising resource element groups that are non-colocated with a
second resource pattern; receiving a channel quality estimate
reference signal (CSI-RS) according to the first resource pattern;
and performing a channel quality estimate based on the channel
state information reference signal.
38. The apparatus of claim 37, wherein the processor is further
configured for receiving one of a user equipment reference signal
and a common reference signal according to the second resource
pattern.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application claims the benefit of priority from
U.S. Provisional Patent Application Ser. No. 61/249,906, entitled
"METHOD AND APPARATUS FOR USING A CHANNEL SPATIAL INFORMATION
REFERENCE SIGNAL IN A WIRELESS COMMUNICATION SYSTEM," filed on Oct.
8, 2009, and U.S. Provisional Application Ser. No. 61/257,187,
entitled "METHOD AND APPARATUS FOR USING A CHANNEL SPATIAL
INFORMATION REFERENCE SIGNAL IN A WIRELESS COMMUNICATION SYSTEM,"
filed on Nov. 2, 2009, both of which are hereby incorporated by
reference in their entirety.
BACKGROUND
[0002] I. Technical Field
[0003] The present disclosure relates generally to communication,
and more specifically to techniques for transmitting a reference
signal in a wireless communication system.
[0004] II. Background
[0005] Wireless communication systems are widely deployed to
provide various communication content such as voice, video, packet
data, messaging, broadcast, etc. These wireless systems may be
multiple-access systems capable of supporting multiple users by
sharing the available system resources. Examples of such
multiple-access systems include Code Division Multiple Access
(CDMA) systems, Time Division Multiple Access (TDMA) systems,
Frequency Division Multiple Access (FDMA) systems, Orthogonal FDMA
(OFDMA) systems, and Single-Carrier FDMA (SC-FDMA) systems.
[0006] In wireless communication systems, such as the Release 8 and
Release 9 versions of the Long Term Evolution (LTE) standard
(referred to as Rel-8 and Rel-9), signal transmissions are defined
for up to four-antenna transmission configurations. With an
increased demand to support higher data rates and throughput
(system capacity), wireless systems with a higher number of
transmission antennas (e.g., eight) have recently received
attention. To accommodate the increased number of transmission
antennas and to further improve system performance, certain
additional reference signal transmissions, e.g., the channel state
(or spatial) Information reference signal (CSI-RS), have recently
been proposed.
[0007] However, introducing such new reference signals raises
issues related to available transmission bandwidth and coexistence
with legacy (e.g., Rel-8 and Rel-9) reference signals. Furthermore,
the introduction of new reference signals raises the issue of
backward compatibility with user equipment not designed to operate
with the new reference signals.
[0008] A better method and system for implementing the channel
state information reference signal are needed.
SUMMARY
[0009] The disclosed designs meet the above-discussed, and other,
needs for using new reference signals, such as CSI-RS, in a
wireless communication system.
[0010] The following presents a simplified summary in order to
provide a basic understanding of some aspects of the disclosed
aspects. This summary is not an extensive overview and is intended
to neither identify key or critical elements nor delineate the
scope of such aspects. Its purpose is to present some concepts of
the described features in a simplified form as a prelude to the
more detailed description that is presented later.
[0011] In one aspect, a method for wireless communication is
disclosed. The method includes selecting a first resource pattern
comprising resource elements, the first resource pattern being
non-colocated with a second resource pattern, and allocating the
first resource pattern to a plurality of antennas for transmitting
a channel state information reference signal (CSI-RS).
[0012] In another aspect, an apparatus for wireless communication
comprising means for selecting a first resource pattern comprising
resource elements, the first resource pattern being non-colocated
with a second resource pattern and means for allocating the first
resource pattern to a plurality of antennas for transmitting a
channel state information reference signal (CSI-RS) is
disclosed.
[0013] In another aspect, an apparatus for wireless communication
is disclosed which includes a processor configured for selecting a
first resource pattern comprising resource elements, the first
resource pattern being non-colocated with a second resource pattern
and allocating the first resource pattern to a plurality of
antennas for transmitting a channel state information reference
signal (CSI-RS).
[0014] In another aspect, a computer program product is provided
with includes a computer-readable storage medium comprising
instructions for causing at least one computer to select a first
resource pattern comprising resource elements, the first resource
pattern being non-colocated with a second resource pattern and
instructions for causing the at least one computer to allocate
allocating the first resource pattern to a plurality of antennas
for transmitting a channel state information reference signal
(CSI-RS).
[0015] In another aspect, a method for wireless communication is
disclosed. The method comprises coordinating, with a base station
of a neighboring cell, a resource pattern allocated to the
transmission of the reference signal and muting, based on the
coordination, one or more locations of the resource pattern.
[0016] In another aspect, an apparatus for wireless communication
comprising means for coordinating, with a base station of a
neighboring cell, a resource pattern allocated to the transmission
of the reference signal, and means for muting, based on the
coordination, the resource pattern at locations corresponding
resource pattern allocated in the neighboring cell is
disclosed.
[0017] In another aspect, a method for wireless communication
comprising receiving a first resource pattern comprising resource
elements that are non-colocated with a second resource pattern,
receiving a channel state information reference signal (CSI-RS)
according to the first resource pattern and performing a channel
quality estimate based on the channel state information reference
signal is disclosed.
[0018] In another aspect an apparatus for wireless communication,
comprising means for receiving a first resource pattern comprising
resource element groups that are non-colocated with a second
resource pattern, means for receiving a channel state information
reference signal (CSI-RS) according to the first resource pattern
and means for performing a channel quality estimate based on the
channel state information reference signal is disclosed.
[0019] In another aspect, a computer program product, comprising a
non-volatile computer-readable medium comprising instructions for
causing at least one computer to receive a first resource pattern
comprising resource element groups that are non-colocated with a
second resource pattern, instructions for causing the at least one
computer to receive a channel state information reference signal
(CSI-RS) according to the first resource pattern and instructions
for causing the at least one computer to perform a channel quality
estimate based on the channel state information reference signal is
disclosed.
[0020] In another aspect, an apparatus for wireless communication
is disclosed which includes a processor configured for storing
instructions for receiving a first resource pattern comprising
resource element groups that are non-colocated with a second
resource pattern, receiving a channel state information reference
signal (CSI-RS) according to the first resource pattern and
performing a channel quality estimate based on the channel state
information reference signal.
[0021] Various aspects and features of the disclosure are described
in further detail below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The features, nature, and advantages of the present
disclosure will become more apparent from the detailed description
set forth below when taken in conjunction with the drawings in
which like reference characters identify correspondingly throughout
and wherein:
[0023] FIG. 1 illustrates an exemplary wireless communication
system.
[0024] FIG. 2 illustrates an exemplary transmission structure.
[0025] FIG. 3 illustrates a resource allocation pattern for a
normal cyclic prefix (CP) subframe.
[0026] FIG. 4 illustrates a resource allocation pattern for an
extended CP subframe.
[0027] FIG. 5 illustrates another resource allocation pattern for a
normal CP subframe.
[0028] FIG. 6 illustrates yet another resource allocation pattern
for a normal CP subframe.
[0029] FIG. 7 illustrates another resource allocation pattern for
an extended CP subframe.
[0030] FIG. 8 illustrates yet another resource allocation pattern
for a normal CP subframe.
[0031] FIG. 9 illustrates yet another resource allocation pattern
for a normal CP subframe.
[0032] FIG. 10 illustrates a process for wireless
communication.
[0033] FIG. 11 illustrates an apparatus for wireless
communication.
[0034] FIG. 12 illustrates another process for wireless
communication.
[0035] FIG. 13 illustrates a base station apparatus for wireless
communication.
[0036] FIG. 14 illustrates yet another process for wireless
communication.
[0037] FIG. 15 illustrates a user equipment apparatus for wireless
communication.
[0038] FIG. 16 illustrates a transmission apparatus for wireless
communication.
DETAILED DESCRIPTION
[0039] Various aspects are now described with reference to the
drawings. In the following description, for purposes of
explanation, numerous specific details are set forth in order to
provide a thorough understanding of one or more aspects. It may be
evident, however, that the various aspects may be practiced without
these specific details. In other instances, well-known structures
and devices are shown in block diagram form in order to facilitate
describing these aspects.
[0040] The techniques described herein may be used for various
wireless communication systems such as CDMA, TDMA, FDMA, OFDMA,
SC-FDMA and other systems. The terms "system" and "network" are
often used interchangeably. A CDMA system may implement a radio
technology such as Universal Terrestrial Radio Access (UTRA),
CDMA2000, etc. UTRA includes Wideband CDMA (WCDMA) and other
variants of CDMA. CDMA2000 covers IS-2000, IS-95 and IS-856
standards. A TDMA system may implement a radio technology such as
Global System for Mobile Communications (GSM). An OFDMA system may
implement a radio technology such as Evolved UTRA (E-UTRA), Ultra
Mobile Broadband (UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX),
IEEE 802.20, Flash-OFDM.RTM., etc. UTRA and E-UTRA are part of
Universal Mobile Telecommunication System (UMTS). 3GPP Long Term
Evolution (LTE) and LTE-Advanced (LTE-A) are new releases of UMTS
that use E-UTRA, which employs OFDMA on the downlink and SC-FDMA on
the uplink. UTRA, E-UTRA, UMTS, LTE, LTE-A and GSM are described in
documents from an organization named "3rd Generation Partnership
Project" (3GPP). CDMA2000 and UMB are described in documents from
an organization named "3rd Generation Partnership Project 2"
(3GPP2). The techniques described herein may be used for the
systems and radio technologies mentioned above as well as other
systems and radio technologies. For clarity, certain aspects of the
techniques are described below for LTE, and LTE terminology is used
in much of the description below.
[0041] The DL PHY channels may include: Physical Downlink Shared
Channel (PDSCH), Physical Broadcast Channel (PBSH), Physical
Multicast Channel (PMCH), Physical Downlink Control Channel
(PDCCH), Physical Hybrid Automatic Repeat Request Indicator Channel
(PHICH), and Physical Control Format Indicator Channel
(PCFICH).
[0042] The UL PHY Channels may include: Physical Random Access
Channel (PRACH), Physical Uplink Shared Channel (PUSCH), and
Physical Uplink Control Channel (PUCCH).
[0043] While various designs are discussed below with reference to
CSI-RS, it is understood that CSI-RS is only an illustrative
example of an additional reference signal that may be introduced to
a wireless communication system. Therefore, the considerations and
designs provided below are applicable to other known or future
reference signals as well.
[0044] In previous releases of the LTE specification, a single
reference signal was defined for channel quality measurement and
for data demodulation. LTE-A has defined two forms of references
signals for demodulation and channel quality measurement: the
demodulation reference signal (DM-RS) and the channel state
information reference signal (CSI-RS). A base station (eNodeB or
eNB) may schedule and transmit these reference signals to UEs. The
UEs may use CSI-RS to perform channel quality measurements and
provide feedback on the channel quality or spatial properties.
Various properties of CSI-RS, including allocation of transmission
resources, backward compatibility with previously deployed UEs and
the coordination with CSI-RS transmissions in neighboring cells,
are disclosed in greater detail below.
[0045] FIG. 1 illustrates a wireless communication system 100,
which may be an LTE system or some other system. System 100 may
include a number of evolved Node Bs (eNBs) 110 and other network
entities. An eNB 110 may be an entity that communicates with the
UEs and may also be referred to as a base station, a Node B, an
access point, etc. Each eNB 110 may provide communication coverage
for a particular geographic area and may support communication for
the UEs located within the coverage area. To improve capacity, the
overall coverage area of an eNB may be partitioned into multiple
(e.g., three) smaller areas. Each smaller area may be served by a
respective eNB subsystem. In 3GPP, the term "cell" can refer to the
smallest coverage area of an eNB and/or an eNB subsystem serving
this coverage area.
[0046] UEs 120 may be dispersed throughout the system, and each UE
120 may be stationary or mobile. A UE 120 may also be referred to
as a mobile station, a terminal, an access terminal, a subscriber
unit, a station, etc. A UE 120 may be a cellular phone, a personal
digital assistant (PDA), a wireless modem, a wireless communication
device, a handheld device, a laptop computer, a cordless phone, a
wireless local loop (WLL) station, a smart phone, a netbook, a
smartbook, etc.
[0047] LTE utilizes orthogonal frequency division multiplexing
(OFDM) on the downlink and single-carrier frequency division
multiplexing (SC-FDM) on the uplink. OFDM and SC-FDM partition a
frequency range into multiple (K) orthogonal subcarriers, which are
also commonly referred to as tones, bins, etc. Each subcarrier may
be modulated with data. In general, modulation symbols are sent in
the frequency domain with OFDM and in the time domain with SC-FDM.
The spacing between adjacent subcarriers may be fixed, and the
total number of subcarriers (K) may be dependent on the system
bandwidth. For example, K may be equal to 128, 256, 512, 1024 or
2048 for system bandwidth of 1.25, 2.5, 5, 10 or 20 mega-Hertz
(MHz), respectively. The system bandwidth may correspond to a
subset of the K total subcarriers.
[0048] FIG. 2 illustrates a transmission structure 200 for the
downlink in the LTE. The transmission timeline may be partitioned
into units of subframes. Each subframe may have a predetermined
duration, e.g., one millisecond (ms), and may be partitioned into a
number of slots (e.g., two slots). Each slot may cover seven OFDM
symbol periods for a normal cyclic prefix (shown along horizontal
axis 204 in FIG. 2) or six symbol periods for an extended cyclic
prefix (not shown in FIG. 2). A number of transmission resource
blocks may be defined for each slot. Each resource block may cover
12 subcarriers (depicted along vertical axis 202) in one slot. The
number of resource blocks in each slot may be dependent on the
system bandwidth and may range from 6 to 110 for system bandwidth
of 1.25 MHz to 20 MHz, respectively. The available resource blocks
may be assigned to various downlink transmissions. For the extended
cyclic prefix (not shown in FIG. 2), the two slots in one subframe
may include 12 symbol periods with indices of 0 through 11.
[0049] In some designs, a resource element (RE) 206 may be a unit
of transmission resource scheduled for downlink transmissions. In
some designs, one RE 206 may correspond to one symbol (or codeword)
of downlink transmission. The REs 206 made available for downlink
transmission of a particular signal may form a "pattern," when
depicted along a two-dimensional grid, such as depicted in FIG. 2.
The assignment of REs for transmission of a signal may therefore be
referred to as the pattern of transmission of that signal.
Furthermore, the term "location of an RE" may refer to the time
(OFDM symbol) and frequency (subcarrier) associated with one of the
RE within a subframe or a resource block, or may informally refer
to the position of the RE 206 in a two-dimensional representation
of transmission resources available in a subframe or a resource
block, e.g., as shown in FIG. 2.
[0050] The transmission overhead associated with CSI-RS may need to
trade off both LTE-A and legacy LTE performance. To assign
transmission resources, e.g., REs 206, for transmission of CSI-RS,
an eNB 110 may perform a trade-off between the effectiveness of
CSI-RS for improving channel performance and the impact of the
reduced availability of transmission resources for data traffic. In
particular, CSI-RS may puncture or take away transmission resources
from data transmission for legacy UEs 120. Therefore, increasing
the overhead of CSI-RS may degrade performance or data transmission
rate to legacy UEs 120. On the other hand, if CSI-RS is allocated
too few transmission resources, a receiver may not be able to
perform adequate channel estimation based on the received CSI-RS.
Therefore, CSI-RS transmissions may be transmitted often (e.g.,
between 2 to 10 milliseconds) and covering a sufficient frequency
range (e.g., the bandwidth of the entire channel) to provide an
adequate channel estimation performance for different single-cell
and multi-cell transmission schemes.
[0051] In some designs, the transmission resource issue may be
addressed by controlling a density of REs 206 allocated to CSI-RS
transmissions. The term "density" here refers to a measure of how
many of the total available transmission resources (e.g., tones,
time slots or codes) are allocated to the transmission of CSI-RS.
In some designs, the density of transmission resources may be
controlled by limiting the number of REs 206 allocated for CSI-RS
transmission in a resource block (RB). In some designs, the density
of transmission resources may be controlled by adjusting the duty
cycle of CSI-RS transmissions. The term "duty cycle" refers to the
periodicity of CSI-RS transmissions. For example, a 2 millisecond
(ms) duty cycle may mean that CSI-RS is transmitted once every 2
ms. In some designs, the density of transmission resources may be
controlled by limiting the number of subframes comprising CSI-RS
transmissions. These and other aspects of controlling the density
of CSI-RS transmission resources are described in greater detail
below.
[0052] A study has shown that CSI-RS with frequency density of 2
RE/RB and 10 ms duty cycle may provide reasonable LTE-A performance
for single user MIMO (SU-MIMO). Some studies have suggested that
densities higher than 2 RE/RB per antenna port may result in a
significant loss of UE performance, especially for a modulation and
coding scheme (MCS) with high coding rate. In some designs, a
scheduler at the eNB 110 may reduce the impact of performance loss
for legacy UEs 120 by taking into account the loss in performance
in rate prediction of the scheduled UE 120 based on the
transmission density of CSI-RS. In some designs, the eNB 110 may
schedule legacy UEs 120 with the requested MCS with lower coding
rates. In some designs the eNB 110, to avoid CSI-RS transmissions
from impacting legacy UE 120, may schedule only LTE-A users in
subframes in which CSI-RS is transmitted. In some designs, a
frequency density of 2 RE/RB per antenna port may be a reasonable
tradeoff between performance and overhead. In other designs, a
fixed density of 1 RE/RB may be a reasonable tradeoff. The number
of RE/RB per antenna port allocated to CSI-RS may be a fixed,
predetermined number. Note that a fixed quota of RE per RB simply
implies allocating a certain number of REs in the RB in which
CSI-RS transmission is scheduled, and may not mean that every RB
scheduled by the eNB 110 includes that many REs for CSI-RS
transmissions.
[0053] As will be discussed below, in some designs, a particular
density number may be mapped to a particular frequency spacing
between allocated REs. For example, in certain designs provided
below, a density of 2 RBs/RE may correspond to a frequency spacing
of 6 subcarriers between CSI-RS REs 206. It may be appreciated that
this spacing is similar to the Rel-8 common (or cell-specific)
reference signal (CRS) spacing. In certain designs, having a
subcarrier spacing similar to CRS may make it possible to leverage
a CRS demodulation structure at a receiver for demodulating
CSI-RS.
[0054] In some designs, the duty cycle of CSI-RS may be
configurable in a (semi)static way to a limited set of values,
e.g., 2, 5 or 10 ms. The operational value of the duty cycle may be
signaled to an LTE-A UE 120 through an information block in a
broadcast channel. In some designs, a different duty cycle may be
specified for each antenna port. In some designs, the same value of
duty cycle may be defined for all antenna ports defined in a cell.
Using the same value of duty cycle may reduce signaling overhead
and computational complexity associated with simultaneously
scheduling and using different duty cycle values for different
antenna ports.
[0055] FIG. 3 depicts a normal CP subframe 300, with the horizontal
axis 302 representing symbols transmitted (time) and the vertical
axis 304 representing frequency. As discussed previously, each
"tile" of the subframe 300 may therefore represent a single RE 206
available for transmission. In some designs, a transmission in an
RE 206 may further be code division multiplexed with another
transmission in the same RE 206.
[0056] In LTE systems, certain REs 206 have been allocated to
transmission of control signals (e.g., control region) at the start
of each subframe. In FIG. 3, the REs 206 corresponding to these
allocated REs 206 are hatch-marked. Although the control region is
shown to span 3 OFDM symbols in the present example, it is
understood that the control region may span a different number of
OFDM symbols in other examples. Additionally, certain REs 206 are
allocated to a Common (or Cell-Specific) Reference Signal (CRS).
The CRS is shifted in positions, based on an identity of the eNB
110 of a particular cell, in RBs. In FIG. 3, the tiles marked "C"
represent REs 206 that may be used for CRS transmission.
Furthermore, REs 206 allocated to transmission of demodulation
reference signals (DM-RS) (also referred to as UE-specific
reference signal or UE-RS), in LTE Release 9, are marked as "D." In
some designs, the REs 206, so allocated to other control and
reference signals, may not be allocated to CSI-RS. One of ordinary
skill in the art would understand that REs 206 being allocated to
transmission of a certain control or reference signal need not mean
that the control/reference signal is present in every scheduled RB,
but simply mean that when the particular control/reference signal
is transmitted, it will be transmitted in one or more of the
allocated RE locations. Accordingly, in certain designs, only RE
regions marked 306, 308, 310, 312, 314 and 316 may be available for
the transmission of CSI-RS. In certain designs, because CRS are
transmitted with a cell dependent offset, an entire OFDM symbol
(hatch-marked) in which a CRS is presented may be avoided for the
transmission of CSI-RS. This helps prevent CSI-RS colliding with
CRS of neighboring cells in a synchronous network.
[0057] FIG. 4 depicts an extended CP subframe 400, showing REs 206
assigned to DM-RS and CRS, marked with "D" and "C," respectively.
As discussed previously, REs 206 in the regions 402, 404, 406, 408,
410, 414, 416, 418 and 420 may be available for CSI-RS
transmissions. The DM-RS REs 206 shown in FIG. 4 may correspond to
the DM-RS REs for rank 2 in LTE Release 9. In general, other DM-RS
locations are also possible. Note that the depicted DM-RS density
for normal CP subframe 300 (FIG. 3) is 24 RE/RB and is 32 RE/RB for
the extended CP subframe 400. In these designs, the maximum number
of available REs 206 for CSI-RS transmission may therefore be 60
and 40 RE/RB for normal and extended CP subframes,
respectively.
[0058] With reference to FIG. 5, a subframe 500 that includes REs
206 allocated to yet another reference signal is shown. Certain
designs may additionally avoid collision of CSI-RS with symbols
that could be used for Rel-8 downlink reference signal (DRS) (also
referred to as UE-specific reference signal or UE-RS), depicted as
tiles "R" in FIG. 5. The DRS signals are transmitted in TDD mode
and the locations (REs 206 used) for DRS depend on cell ID. In such
designs, then the number of available REs 206 for CSI-RS may reduce
to 24 REs, depicted as regions 502, 504, 506, 508 and 510 in the
subframe 500 of FIG. 5. Alternatively, in some other designs only
REs 206 used by DRS during an actual allocation/transmission may be
excluded instead of excluding the entire RE location. In other
words, the CSI-RS pattern for each cell may be initialized to not
overlap with DRS pattern of that particular cell.
[0059] From FIGS. 3, 4 and 5, it may be seen that, in designs that
avoid co-location with patterns used for other reference signals
and legacy reference signals, the number of REs 206 available for
CSI-RS may be limited to a smaller subset. In some designs, REs 206
allocated to CSI-RS transmissions from a particular antenna port
may be selected from among all available CSI-RS RE 206 locations to
achieve a uniform spacing of transmissions from the particular
antenna port across the frequency range. The uniform spacing
constraint may further limit the total number of REs 206 available
for CSI-RS transmissions from all antenna ports. In designs where
CSI-RS is uniformly spaced across the frequency range, demodulation
of CSI-RS may be simplified, as previously discussed. Furthermore,
using uniformly spaced REs 206 for transmission of CSI-RS may
provide a more accurate channel quality estimate over the entire
frequency range. In some designs, REs 206 allocated to CSI-RS
corresponding to a particular antenna port may be uniformly spaced
in frequency. Thus, in certain designs, CSI-RS port of a cell may
be allocated uniformly spaced subcarriers in one given symbol.
[0060] In certain designs, REs 206 allocated to DM-RS may be
excluded from CSI-RS (e.g., as shown in FIGS. 3 and 4). As
previously discussed, this may further reduce the number of
available REs for CSI-RS transmissions. For example, in the
subframe 300, the number of available REs 206 for CSI-RS may be
reduced to 36. To remedy the reduction in available REs 206 for
CSI-RS transmissions, in some designs that exclude DM-RS symbols,
the number of CRS antenna ports may be limited to 2. By limiting
the number of CRS antenna ports to 2, the OFDM symbol containing
CRS for antenna ports 2 and 3 may be used for CSI-RS transmissions.
This re-allocation of CRS may increase the number of available
CSI-RS symbols to 48 in a normal subframe.
[0061] Referring now to FIGS. 6 and 7, in particular, the above
property can also provide a uniform structure for CSI-RS for
extended CP and normal CP subframes. For a design that uses 2 RE/RB
allocation to CSI-RS, it is possible to group the available REs 206
into groups of REs 206 (e.g., pairs as depicted in FIGS. 6 and 7).
Each pair includes two REs 206 in the same RB with the same
frequency spacing (e.g., frequency spacing 6 subcarriers in FIGS. 6
and 7). For example, FIG. 6 illustrates pairing of REs 206, as
shown in FIG. 3. REs 206 with same numbers in FIG. 6 may form a
pair, and may be spaced 6 subcarriers apart with respect to each
other and also with respect to the corresponding REs 206 in an
adjacent RB (not shown in FIG. 6). In other words, when contiguous
RBs are assigned to CSI-RS transmissions, the pattern of RE 206
allocation may be uniform not just within one RB, but across
multiple RBs as well (i.e., uniformity along both horizontal and
vertical axes in FIG. 6). As can be seen from FIG. 6, 26 pairs of
REs 206 may be possible with a frequency spacing of 6, with 52 REs
from 60 available REs depicted in FIG. 3 being used for CSI-RS. It
will be appreciated that if 1 RE/RB per port is assigned to CSI-RS,
each available RE 206 in FIG. 6 (total 60 REs 206) may be assigned
a unique number from 1 to 60 and may be available for assignment to
an antenna port.
[0062] FIG. 7 illustrates another pairing example in which 20 RE
pairs are formed using all 40 available REs 206 depicted in FIG. 4
for an extended CP subframe. In certain designs, each RE pair may
be used for one CSI-RS antenna port per RB.
[0063] It will be appreciated that while a given cell may need a
limited number of REs 206 for CSI-RS transmissions (for example, an
8-antenna configuration needs 8 assignments, one per antenna port),
the available REs 206 depicted in FIG. 6 or 7 could be shared among
neighboring cells such that the eNBs 110 of neighboring cells do
not use the same REs 206. For example, with reference to FIG. 6,
one eNB 110 may use REs 206 numbered 1 to 8, while a neighboring
eNB 110 may use REs 206 numbered 9 to 16 for CSI transmissions.
Therefore, neighboring cells may be able to avoid CSI-RS collisions
by coordinating RE allocation among the eNBs 110.
[0064] FIG. 8 illustrates an example subframe 800, wherein four RE
pairs 802, 804, 806 and 808 that may be assigned to CSI-RS antenna
ports. The RE pairs 802, 804, 806 and 808 may be chosen to have
uniform spacing across both frequency and time. The uniform
assignment, as depicted in subframe 800, may help avoid
disproportionate "crowding" of REs 206, burdening legacy UE 120
transmissions in some subframes. This may ensure that CSI-RS
punctures all codeblocks substantially equally for legacy UEs 120
that are scheduled with more than one codeblock.
[0065] In certain designs, the assigned locations of RE pairs for
CSI-RS may be cell-dependent and may be initialized as a function
of a physical cell ID and number of CSI-RS antenna ports.
Therefore, in certain designs, the OFDM symbols with available REs
206 for CSI-RS may be partitioned into two sets: a first set having
the first slot of a subframe and the other group having the second
slot of the subframe. In certain designs, to reduce impact on data
traffic of legacy UEs 120, the initialization procedure of the
CSI-RS pattern may ensure that the OFDM symbols used for CSI-RS
transmissions alternate between the two partitions of the OFDM
symbols, or equivalently two slots, as described above.
[0066] Referring now to FIG. 9, an example resource assignment is
shown for a normal subframe 900. In the depicted example subframe
900, CSI-RS locations of a given antenna port may occupy evenly
spaced subcarriers in different OFDM symbols. The REs 206 available
for CSI-RS transmission are numbered from 1 to 12. For a desired
uniform frequency spacing (e.g., 6 in this example), two REs 206
having the desired uniform spacing (e.g., 6 in this example) may be
assigned to CSI-RS. For example, any RE 206 with number 1 can be
paired with any RE 206 with number 7 and represent the locations
for transmission of one CSI-RS antenna port. Four pairs of REs:
902, 904, 906 and 908, are depicted in the normal subframe 900. The
pairs 902, 904, 906 and 908 are uniformly spaced across both
horizontal (time) and vertical (frequency) axes 302, 304.
[0067] Still referring to FIG. 9, it may be appreciated that that
the CSI-RS antenna ports can be mapped to different reserved RE 206
locations (cross-hatched tiles in FIG. 9) across different resource
blocks as long as the subcarrier spacing between REs 206 used for
each CSI-RS antenna port is uniform with the frequency spacing
required. In certain designs, a different mapping across different
resource blocks and/or subframes may be used to provide the same
number of CSI-RS antenna port REs 206 for all antenna ports within
each OFDM symbol for the purpose of power boosting the reference
signal.
[0068] In certain designs, CSI-RS may be transmitted on multiple
subframes within a given frame (as opposed to transmitting in a
single subframe). In such designs, CSI-RS for different antenna
ports of the same cell or CSI-RS across different cells may be
transmitted in different sub-frames. In one aspect, the collision
rate of CSI-RS across different cells may be probabilistically
reduced. Furthermore, the eNB 110 may have more flexibility in the
placement and the pattern of REs 206 allocated to CSI-RS. For
example, when transmission is organized as frames comprising 10
subframes numbered 0 to 9, in certain designs, CSI-RS transmissions
may occur only in subframe #0. In other designs, CSI-RS
transmissions may be scheduled in more subframes--e.g., subframes 0
and 1.
[0069] However, using multiple sub-frames for CSI-RS transmission
may require a trade-off due to possible impact on the performance
of legacy UEs 120. For example, taking away REs 206 from many
subframes may puncture the data region of legacy UEs 120 in
multiple sub-frames, resulting in a system performance loss. Some
designs may therefore limit the impact of puncturing legacy UE 120
data region to a predetermined number of CSI-RS carrying sub-frames
so that eNB 110 may schedule data transmissions around these
subframes by scheduling only LTE-A UEs 120 in these subframes or
scheduling legacy UEs 120 with a lower rate in these subframes.
[0070] Furthermore, limiting CSI-RS transmission to a predetermined
number of subframes may also enable better battery life management
in UEs 120. For example, if CSI-RS from different antenna ports in
a cell or from multiple cells are transmitted in subframes 1 and 6,
then a UE 120 may have to wake up twice within a frame to receive
and process CSI-RS transmissions. However, if all CSI-RS are
transmitted in subframe 1, then a UE 120 may have to wake up only
for one subframe, avoiding having to wake up frequently to measure
CSI-RS from multiple cells or different antenna ports in different
subframes.
[0071] Therefore, in certain designs, the transmission of CSI-RS
may be restricted to a limited number of subframes, referred to as
CSI-RS subframes. The number of CSI-RS subframes may be selected
based on a desired CSI-RS collision rate across different cells.
For example, restricting CSI-RS transmissions from all cells to the
same subframe may result in a higher probability of collision, but
may help improve battery performance of UEs 120, as discussed
above. In certain designs, subframes that include PBCH, sync
signals or paging within a radio frame from the CSI-RS subframe
set, i.e. subframes {0, 4, 5, 9} in FDD mode, may be excluded from
carrying CSI-RS, to avoid potential interference with these control
signals.
[0072] In certain designs, when the number of CSI-RS subframes is
greater than 1, the CSI-RS subframes used by neighboring eNBs 110
may be coordinated to be contiguous (e.g., subframe number 0 and 1)
allowing a UE 120 to measure CSI-RS signals from different eNBs 110
in a single wake up cycle. Furthermore, CSI-RS transmissions from
different eNBs 110 may be coordinated so that the number of
contiguous subframes used may be limited to as small a number as
possible. For example, if CSI-RS resources are available on one
subframe in which another eNB is transmitting its CSI-RS, then a
second eNB 110 may perform its CSI-RS transmissions on the same
subframe instead of selecting another subframe for its CSI-RS
transmissions.
[0073] In certain designs, CSI-RS transmissions from different
antenna ports of the same cell may be orthogonally multiplexed. For
example, with reference to FIG. 8, RE with index 11 in the region
804 and the neighboring RE with index 10 may both be used for
CSI-RS transmission of two antenna ports (1 and 2). However, these
two transmissions may be code division multiplexed to be orthogonal
to each other.
[0074] As previously described with respect to FIG. 1, multiple
eNBs 110 may be present in the wireless communication system 100.
In certain designs, the multiple eNBs 110 may coordinate with each
other the CSI-RS transmissions within each respective cell. The
coordination may include two operations: "muting" and "hopping," as
further described below.
[0075] The pattern of REs 206 allocated to CSI-RS transmissions in
a cell may be hopped, or altered, to randomize occurrence of CSI-RS
signals across different cells, to reduce a rate of collision. In
situations of dominant interferer cell collision, hopping may
advantageously avoid interference by the dominant eNB 110. For
example, when there is no hopping, if CSI-RS of a cell collides
with CSI-RS of a dominant interferer once, it may always collide,
making it impossible for a UE 120 to obtain accurate CSI
measurements from the CSI-RS. However, if the patterns are hopping
it is quite likely that they do not collide on some occasions,
which gives an opportunity to the UE 120 to estimate the CSI
reliably using the CSI-RS of the weaker cells. In various designs,
hopping patterns may be chosen as a function of the system time,
the antenna port index, the physical cell ID or a combination of
these parameters. For example, in some designs, each CSI-RS port
may be assigned a frequency offset, a symbol index from the set of
available symbols and a subframe index from the set of CSI-RS
subframes. When 2 REs/RB per antenna port are assigned for CSI-RS
transmission in each subframe, the CSI-RS port can be assigned to a
different RE pair, as a random function of the above
parameters.
[0076] In one design, the assignment of an antenna port to an RE
pair index (e.g., 1 to 26, as shown in FIG. 5) may be carried out
by randomly choosing from 1 to 26 in each subframe that a CSI-RS
transmission may be present in. The subframe containing CSI-RS may
be randomly chosen. The random hopping may be generated by a
pseudo-random sequence generator that takes physical cell ID,
system time and possibly antenna port index into account. In
certain designs, the hopping function or the pseudo-random sequence
may be chosen to preserve orthogonality across CSI-RS antenna ports
of the same cell.
[0077] A hopping pattern may also be advantageously used to provide
a higher frequency domain granularity for channel estimation. This
may be especially true for low speed users or in cases where the
duty cycle configured is low (i.e., CSI-RS are transmitted with
large time gaps). For example, without a hopping pattern, to
improve the frequency resolution may take a higher CSI-RS density
in frequency to transmit CSI-RS covering a desired frequency range.
However, using a hopping pattern, the eNB 110 may assign a pattern
that ensures a wide sampling of the frequency domain (with
different offset) for any antenna port. Hence, although the
frequency resolution per look in time is low, the multiple looks in
frequency obtained over time may improve the effective frequency
resolution.
[0078] In certain designs, a hopping pattern may be defined not
only to randomize (or orthogonalize) across the REs 206 within a
subframe but across the REs 206 of all the CSI-RS subframes
collectively. For example, if allocated RE locations for a
particular CSI-RS port are represented as a function of three
parameters: subframe number (SFN), time and frequency, then all
these three parameters may be hopped within their set of possible
values. This hopping, or randomization, may help randomize RE
allocations when CSI-RS subframe set size is larger than one.
[0079] In certain examples, the assigned pattern of CSI-RS REs 206
may be hopped across subframes. In other words, for each cell, the
subframe(s) containing CSI-RS transmissions may be hopped within
the CSI-RS subframes set over time. For example, consider CSI-RS
subframe set {1,2} within a radio frame and assume that the CSI-RS
periodicity is 10 ms. Then in each 10 ms period, the CSI-RS
locations for a particular port and particular cell may be present
in one of the subframes 1 or 2. In some designs, the allocated
subframe (i.e., 1 or 2) may not change over time. For example,
CSI-RS locations for port x, cellID y may always be present in
subframe index 1. In other designs, the subframe assigned to CSI-RS
for port x, cellID y may be hopped (or randomly chosen) every 10
ms, between all possible values of subframe index or number (1 or 2
in this example). The subframe number hopping may be a function of
cell ID, antenna port and CSI-RS subframe set, or a system
time.
[0080] The subframe hopping approach may help reduce collisions of
intercell CSI-RS transmissions. For example, when all CSI-RS for
all antenna ports of a cell in a duty cycle are present in one
subframe chosen from the CSI-RS subframe set and the index of this
subframe is hopped over time depending on the cell ID, among other
parameters (e.g., number of CSI-RS antenna ports, number of CSI-RS
subframes, and system time), then collision rate may be reduced
because CSI-RS of different cells may be present in different
subframes over time. In some designs, the impact on legacy UEs 100
may still be limited to a minimum number of subframes, as discussed
previously, by constraining the total number of subframes used for
CSI-RS transmissions. Furthermore, the computation complexity of
feedback computation may also be reduced by limiting the total
number of subframes of CSI-RS transmissions as above.
[0081] In some designs, two levels of hopping of CSI-RS pattern may
be used. One level may correspond to the hopping of the
frequency/time/code allocation to REs 206 within a subframe, and
the other level may correspond to hopping of the subframe indices
for which a CSI-RS transmission of a particular port and/or cell
may be present. This multi-level hopping may help avoid collisions
between CSI-RS transmissions of different antenna port indices
across different cells.
[0082] In some designs, the hopping mode may be disabled or enabled
in a semi-static or dynamic way. The UE 120 may be informed of the
CSI-RS hopping mode by a higher layer signaling, through a
broadcast or unicast channel, and/or within a layer 2
signaling.
[0083] In certain designs, the choice of enabling/disabling hopping
mode and selecting locations that each cell will use for CSI-RS
transmissions may be dependent on, for example, the transmission
mode, the number of users and their channel quality and
capabilities. For instance, if joint transmission in a multi-cell
setup is employed in a cell, the network may coordinate (by
communication among eNBs 110) the hopping mode and locations of a
subset of cells. In one design, when eNBs 110 coordinate CSI-RS
resources used, hopping may be disabled. It will be appreciated
that each level of the two-level hopping, as described above, may
be disabled independent of the other level. For example, it may be
possible to consider disabling the hopping of the subframe index
disjointly from the hopping of the CSI-RS locations within a
subframe. For instance, in one design, subframe index hopping may
be disabled so that a CSI-RS transmission may be performed only in
subframe 1 in each radio frame but hopping of CSI-RS locations may
be allowed within subframe 1 over a period of time.
[0084] In certain designs, one or more parameters regarding hopping
schedule (e.g., time instances when hopping is turned on/off or a
next CSI-RS pattern will be utilized, and so on) may be signaled
from an eNB 110 to a UE 120. The hopping scheduling parameters may
help the UE 120 identify the hopping schedule for the CSI-RS
transmission.
[0085] In some designs, the available CSI-RS locations for each
cell can be limited to a subset of all the available CSI-RS
locations (e.g. depicted in FIG. 5). This subset may be different
for different cells and may be changing over time. In addition,
eNBs 110 may coordinate among each other at a higher layer (e.g.,
layer 3), the subset of REs within a subframe used by each eNB
110.
[0086] Certain designs, such as designs that use CSI-RS in
coordinated multipoint transmission (CoMP) configurations, may
perform "muting" of CSI-RS transmissions. For example, eNB 110 of a
cell may not perform any transmissions at locations of RE 206
assigned to CSI-RS transmissions in a neighboring cell. It may be
possible to improve the channel estimation performance of CSI-RS,
or equivalently reduce the overhead for a given performance by
performing this muting operation. Because of muting of other
signals that may potentially interfere with CSI-RS transmissions of
a given cell, estimation of channel state information from
non-serving cells or weaker serving cells may be significantly
improved. Information needed (e.g., RE locations) for traffic
puncturing (muting) may be signaled between eNBs 110. Additionally,
UEs 120 within a cell may be informed of the data muting by the eNB
110 to make the UEs 120 aware that data is not being transmitted to
those UEs 120 and to avoid potential interference of data
transmissions with another cell's CSI-RS transmissions.
[0087] FIG. 10 illustrates a process 1000 for wireless
communication. At operation 1002, a first resource pattern
comprising resource elements is selected. The first resource
pattern may comprise, for example, possible RE locations as
described in FIGS. 3 to 7. In certain designs, the resource
elements may be uniformly spaced. The first resource pattern is
non-colocated with a second resource pattern. The second resource
pattern may, for example, comprise RE locations allocated to other
reference signals such as CRS and DM-RS (or UE-RS). At operation
1004, the first resource pattern is allocated to a plurality of
antennas for transmitting a channel state information reference
signal (CSI-RS). The allocation may be performed, for example, as
described with respect to FIGS. 8 and 9. The process 1000 may
further include one or more of the RE allocation techniques
discussed in this disclosure.
[0088] FIG. 11 illustrates an apparatus 1100 for wireless
communication. The apparatus 1100 include a module 1102 to
selecting a first resource pattern comprising resource elements,
the first resource pattern being non-colocated with a second
resource pattern and a module 1104 to allocate the first resource
pattern to a plurality of antennas for transmitting a channel state
information reference signal (CSI-RS). In certain designs, the
first resource pattern may comprise uniformly spaced resource
elements. The first resource pattern may comprise, for example,
possible RE locations as described in FIGS. 3 to 7. The second
resource pattern may, for example, comprise RE locations allocated
to other reference signals such as CRS and DM-RS (or UE-RS). The
allocation may be performed, for example, as described with respect
to FIGS. 8 and 9. The apparatus 1100 may further include modules
for implementing one or more of the designs discussed in this
disclosure.
[0089] FIG. 12 illustrates a process 1202 of wireless communication
of allocating resources to a transmission of a reference signal,
implemented at an eNB. At operation 1204, a resource pattern
allocated to the transmission of the reference signal is
coordinated with a base station of a neighboring cell. The
coordination may include, for example, the muting or the hopping
operation described above. At operation 1206, the resource pattern
at locations corresponding resource pattern allocated in the
neighboring cell is muted based on the coordination. The process
1200 may further include one or more of the techniques discussed in
this disclosure.
[0090] FIG. 13 illustrates a base station apparatus 1300 for
wireless communication. The apparatus 1300 includes a module 1302
for coordinating, with a base station of a neighboring cell, a
resource pattern allocated to the transmission of the reference
signal and a module 1304 for muting, based on the coordination, the
resource pattern at locations corresponding resource pattern
allocated in the neighboring cell. The coordination may include,
for example, the muting or the hopping operation described above.
The apparatus 1300 may further include modules for implementing one
or more of the designs discussed in this disclosure.
[0091] FIG. 14 illustrates a process 1400 of wireless
communication, implemented at a UE. At operation 1402, a first
resource pattern comprising resource elements that are
non-colocated with a second resource pattern is received. The first
resource pattern may, for example, include uniformly spaced
resource elements. At operation 1404, a channel state information
reference signal (CSI-RS) according to the first resource pattern
is received. At operation 1406, a channel quality estimate based on
the channel state information reference signal is performed. The
process 1400 may further include one or more of the techniques
discussed in this disclosure.
[0092] FIG. 15 illustrates a user equipment apparatus 1500 for
wireless communication. The apparatus 1500 comprises module 1502
for receiving a first resource pattern comprising resource element
groups that are non-colocated with a second resource pattern,
module 1504 for receiving a channel state information reference
signal (CSI-RS) according to the first resource pattern and module
1506 for performing a channel quality estimate based on the channel
state information reference signal. The apparatus 1300 may further
include modules for implementing one or more of the designs
discussed in this disclosure.
[0093] FIG. 16 illustrates a block diagram of a design of an
exemplary base station/eNB 110 and a UE 120, which may be one of
the eNBs and one of the UEs in FIG. 1, where the various processes
disclosed above may be implemented, as appropriate. The UE 120 may
be equipped with T antennas 1234a through 1234t, and the base
station 110 may be equipped with R antennas 1252a through 1252r,
where in general T.gtoreq.1 and R.gtoreq.1.
[0094] At UE 120, a transmit processor 1220 may receive data from a
data source 1212 and control information from a
controller/processor 1240. Transmit processor 1220 may process
(e.g., encode, interleave, and symbol map) the data and control
information and may provide data symbols and control symbols,
respectively. Transmit processor 1220 may also generate one or more
demodulation reference signals for multiple non-contiguous clusters
based on one or more RS sequences assigned to UE 120 and may
provide reference symbols. A transmit (TX) multiple-input
multiple-output (MIMO) processor 1230 may perform spatial
processing (e.g., precoding) on the data symbols, the control
symbols, and/or the reference symbols from transmit processor 1220,
if applicable, and may provide T output symbol streams to T
modulators (MODs) 1232a through 1232t. Each modulator 1232 may
process a respective output symbol stream (e.g., for SC-FDMA, OFDM,
etc.) to obtain an output sample stream. Each modulator 1232 may
further process (e.g., convert to analog, amplify, filter, and
upconvert) the output sample stream to obtain an uplink signal. T
uplink signals from modulators 1232a through 1232t may be
transmitted via T antennas 1234a through 1234t, respectively.
[0095] At base station 110, antennas 1252a through 1252r may
receive the uplink signals from UE 120 and provide received signals
to demodulators (DEMODs) 1254a through 1254r, respectively. Each
demodulator 1254 may condition (e.g., filter, amplify, downconvert,
and digitize) a respective received signal to obtain received
samples. Each demodulator 1254 may further process the received
samples to obtain received symbols. A channel processor/MIMO
detector 1256 may obtain received symbols from all R demodulators
1254a through 1254r. Channel processor 1256 may derive a channel
estimate for a wireless channel from UE 120 to base station 110
based on the demodulation reference signals received from UE 120.
MIMO detector 1256 may perform MIMO detection/demodulation on the
received symbols based on the channel estimate and may provide
detected symbols. A receive processor 1258 may process (e.g.,
symbol demap, deinterleave, and decode) the detected symbols,
provide decoded data to a data sink 1260, and provide decoded
control information to a controller/processor 1280.
[0096] On the downlink, at base station 110, data from a data
source 1262 and control information from controller/processor 1280
may be processed by a transmit processor 1264, precoded by a TX
MIMO processor 1266 if applicable, conditioned by modulators 1254a
through 1254r, and transmitted to UE 120. At UE 120, the downlink
signals from base station 110 may be received by antennas 1234,
conditioned by demodulators 1232, processed by a channel
estimator/MIMO detector 1236, and further processed by a receive
processor 1238 to obtain the data and control information sent to
UE 120. Processor 1238 may provide the decoded data to a data sink
1239 and the decoded control information to controller/processor
1240.
[0097] Controllers/processors 1240 and 1280 may direct the
operation at UE 120 and base station 110, respectively. Processor
1220, processor 1240, and/or other processors and modules at UE 120
may perform or direct process 1400 in FIG. 14 and/or other
processes for the techniques described herein. Processor 1256,
processor 1280, and/or other processors and modules at base station
110 may perform or direct process 1202 in FIG. 12 and/or other
processes for the techniques described herein. Memories 1242 and
1282 may store data and program codes for UE 120 and base station
110, respectively. A scheduler 1284 may schedule UEs for downlink
and/or uplink transmission and may provide allocations of resources
(e.g., assignment of multiple non-contiguous clusters, RS sequences
for demodulation reference signals, etc.) for the scheduled
UEs.
[0098] It will be appreciated that several properties of CSI-RS
transmissions are disclosed herein. In certain designs, CSI-RS
pattern (i.e., the pattern or REs within a subframe, assigned to
the transmission of CSI-RS signal) may cell-specific. The pattern
of CSI-RS transmissions may depends on the number of antenna ports,
a physical cell ID of the particular cell and so on. In certain
designs, the transmission overhead associated with CSI-RS may be
controlled by selecting an appropriate duty cycle of transmission.
In certain designs, the transmission overhead associated with
CSI-RS may be controlled by limiting the number of REs assigned per
RB to CSI-RS transmissions.
[0099] In will further be appreciated that several techniques of
limiting impact of CSI-RS transmissions on legacy equipment are
disclosed. For example, in certain designs, CSI-RS transmissions
across different cells may be limited to a small number of
subframes, thereby reducing impact on wake up time of a UE 120 and
puncturing of data traffic to legacy UEs 120. In certain designs,
CSI-RS is not transmitted on a subframe of a radio frame which
transmits a paging, or a PBCH or a sync signal.
[0100] It will further be appreciated that the disclosed designs
enable efficient implementation of CSI-RS framework. For example,
in some designs, the number of CSI-RS ports is statically
configured. In some designs, the duty cycle of the CSI-RS may be
semi-statically configured from a limited set of values, e.g. {2,
5, 10} ms.
[0101] It will further be appreciated that techniques are disclosed
to enable orthogonal transmission of CSI-RS. In some designs,
CSI-RS of an antenna port of a cell may be uniformly spaced in
frequency in one OFDM symbol with a frequency spacing of a fixed
number (e.g., 6) of subcarriers.
[0102] In certain designs, CSI-RS pattern of different antenna
ports of different cells may hop in time. The hopping may be a
function of the physical cell ID, antenna port index and the system
time.
[0103] In certain designs, data/control signal transmissions may be
muted in locations used by CSI-RS transmissions of neighboring
cells. In some designs, the muting may be performed based on
coordination among multiple eNBs 110.
[0104] It will be appreciated that the CSI-RS designs disclosed
herein may be used with any transmission mode, such as a
single-cell single and MU-MIMO and coordinated multi-cell
transmission.
[0105] It will be appreciated that CSI-RS designs as discussed
herein may be embodied to include one or more of the following
aspects, among other aspects disclosed herein:
[0106] (1) CSI-RS of a cell may avoid CRS REs of that cell.
[0107] (2) CSI-RS may entirely avoid CRS symbols to avoid collision
with CRS of neighboring cell(s).
[0108] (3) CSI-RS may avoid UE-specific RS (UE-RS) REs. It should
be noted that the UE specific RS REs refers to any REs that could
be used for UE-RS and may not always be used for UE-RS.
[0109] (4) CSI-RS may avoid UE-RS of one LTE release but not of
another. For example, certain designs may avoid Rel 9/10 UE-RS but
not Rel 8 UE-RS.
[0110] (5) CSI-RS patterns may be chosen such that they avoid UE-RS
REs of any cell.
[0111] (6) CSI-RS pattern for a cell may be chosen such that they
avoid UE-RS REs only of that cell. Because Rel-8 UE-RS pattern is
different for different cell IDs, it may affect the number of
available CSI-RS patterns and the signaling thereof.
[0112] (7) CSI-RS pattern may be chosen to be a function of one or
more of cell ID, number of CSI-RS antenna ports and a type of
subframe in which CSI-RS is transmitted.
[0113] (8) CSI-RS pattern may be chosen to avoid symbols and/or
subframes containing Sync Signals, PBCH or paging.
[0114] (9) CSI-RS of different antenna ports of same cells may be
orthogonally multiplexed.
[0115] (10) CSI-RS of different cells may be orthogonally
multiplexed with respect to each other.
[0116] (11) CSI-RS of neighboring cells may be muted to avoid
collision/interference.
[0117] (12) Muting may be signaled to UEs to avoid transmissions in
muted transmission resources.
[0118] (13) CSI-RS patterns may be hopped across subframes.
[0119] (14) Hopping pattern may be a function of cell ID, subframe
index, and/or other system parameters.
[0120] (15) Hopping may be selectively used and enabling or
disabling of hopping may be signaled to user equipment.
[0121] Those of skill in the art would understand that information
and signals may be represented using any of a variety of different
technologies and techniques. For example, data, instructions,
commands, information, signals, bits, symbols, and chips that may
be referenced throughout the above description may be represented
by voltages, currents, electromagnetic waves, magnetic fields or
particles, optical fields or particles, or any combination
thereof.
[0122] Those of skill would further appreciate that the various
illustrative logical blocks, modules, circuits, and process steps
described in connection with the disclosure herein may be
implemented as electronic hardware, computer software, or
combinations of both. To clearly illustrate this interchangeability
of hardware and software, various illustrative components, blocks,
modules, circuits, and steps have been described above generally in
terms of their functionality. Whether such functionality is
implemented as hardware or software depends upon the particular
application and design constraints imposed on the overall system.
Skilled artisans may implement the described functionality in
varying ways for each particular application, but such
implementation decisions should not be interpreted as causing a
departure from the scope of the present disclosure.
[0123] The various illustrative logical blocks, modules, and
circuits described in connection with the disclosure herein may be
implemented or performed with a general-purpose processor, a
digital signal processor (DSP), an application specific integrated
circuit (ASIC), a field programmable gate array (FPGA) or other
programmable logic device, discrete gate or transistor logic,
discrete hardware components, or any combination thereof designed
to perform the functions described herein. A general-purpose
processor may be a microprocessor, but in the alternative, the
processor may be any conventional processor, controller,
microcontroller, or state machine. A processor may also be
implemented as a combination of computing devices, e.g., a
combination of a DSP and a microprocessor, a plurality of
microprocessors, one or more microprocessors in conjunction with a
DSP core, or any other such configuration.
[0124] The steps of a method or algorithm described in connection
with the disclosure herein may be embodied directly in hardware, in
a software module executed by a processor, or in a combination of
the two. A software module may reside in RAM memory, flash memory,
ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a
removable disk, a CD-ROM, or any other form of storage medium known
in the art. An exemplary storage medium is coupled to the processor
such that the processor can read information from, and write
information to, the storage medium. In the alternative, the storage
medium may be integral to the processor. The processor and the
storage medium may reside in an ASIC. The ASIC may reside in a user
terminal. In the alternative, the processor and the storage medium
may reside as discrete components in a user terminal.
[0125] In one or more exemplary designs, the functions described
may be implemented in hardware, software, firmware, or any
combination thereof. If implemented in software, the functions may
be stored on or transmitted over as one or more instructions or
code on a computer-readable medium. Computer-readable media
includes both computer storage media and communication media
including any medium that facilitates transfer of a computer
program from one place to another. A storage media may be any
available media that can be accessed by a general purpose or
special purpose computer. By way of example, and not limitation,
such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM
or other optical disk storage, magnetic disk storage or other
magnetic storage devices, or any other medium that can be used to
carry or store desired program code means in the form of
instructions or data structures and that can be accessed by a
general-purpose or special-purpose computer, or a general-purpose
or special-purpose processor. Disk and disc, as used herein,
includes compact disc (CD), laser disc, optical disc, digital
versatile disc (DVD), floppy disk and blu-ray disc where disks
usually reproduce data magnetically, while discs reproduce data
optically with lasers. Combinations of the above should also be
included within the scope of computer-readable media.
[0126] The previous description of the disclosure is provided to
enable any person skilled in the art to make or use the disclosure.
Various modifications to the disclosure will be readily apparent to
those skilled in the art, and the generic principles defined herein
may be applied to other variations without departing from the
spirit or scope of the disclosure. Thus, the disclosure is not
intended to be limited to the examples and designs described herein
but is to be accorded the widest scope consistent with the
principles and novel features disclosed herein.
[0127] In view of the exemplary systems described supra,
methodologies that may be implemented in accordance with the
disclosed subject matter have been described with reference to
several flow diagrams. While for purposes of simplicity of
explanation, the methodologies are shown and described as a series
of blocks, it is to be understood and appreciated that the claimed
subject matter is not limited by the order of the blocks, as some
blocks may occur in different orders and/or concurrently with other
blocks from what is depicted and described herein. Moreover, not
all illustrated blocks may be required to implement the
methodologies described herein. Additionally, it should be further
appreciated that the methodologies disclosed herein are capable of
being stored on an article of manufacture to facilitate
transporting and transferring such methodologies to computers. The
term article of manufacture, as used herein, is intended to
encompass a computer program accessible from any computer-readable
device, carrier, or media.
[0128] It should be appreciated that any patent, publication, or
other disclosure material, in whole or in part, that is said to be
incorporated by reference herein is incorporated herein only to the
extent that the incorporated material does not conflict with
existing definitions, statements, or other disclosure material set
forth in this disclosure. As such, and to the extent necessary, the
disclosure as explicitly set forth herein supersedes any
conflicting material incorporated herein by reference. Any
material, or portion thereof, that is said to be incorporated by
reference herein, but which conflicts with existing definitions,
statements, or other disclosure material set forth herein, will
only be incorporated to the extent that no conflict arises between
that incorporated material and the existing disclosure
material.
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