Note: Descriptions are shown in the official language in which they were submitted.
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METHODS OF CHANNEL STATE INFORMATION FEEDBACK AND
TRANSMISSION IN COORDINATED MULTI-POINT WIRELESS
COMMUNICATIONS SYSTEM
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to and the benefit of United States
Provisional Patent Application Serial Number 61/523,056 filed August 12, 2011,
United States Provisional Patent Application Serial Number 61/541,387 filed
September 30, 2011, and United States Patent Application Serial Number
13/545,632
filed July 10, 2012, the subject matter of which is incorporated herein by
reference
BACKGROUND OF THE INVENTION
Field of the Invention
[0002] The present disclosure is directed in general to communications
systems
and more particularly, to channel state information feedback and data
transmission in
coordinated multi-point (CoMP) wireless communications systems.
Description of the Related Art
[0003] In known wireless telecommunications systems, transmission equipment
in
a base station or access device transmits signals throughout a geographical
region
which is known as a cell. As technology has evolved, more advanced equipment
has
been introduced that can provide services that were not possible previously.
This
advanced equipment might include, for example, an E-UTRAN (evolved universal
terrestrial radio access network) node B (eNB), a base station or other
systems and
devices. Such advanced or next generation equipment is often referred to as
long-term
evolution (LTE) equipment, and a packet-based network that uses such equipment
is
often referred to as an evolved packet system (EPS). An access device is any
component, such as a traditional base station or an LTE eNB (Evolved Node B),
which can provide user equipment (UE) or mobile equipment (ME) with access to
other components in a telecommunications system.
[0004] Coordinated multi-point (CoMP) transmission and reception is one
solution for providing a more ubiquitous user experience in wireless
communication
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systems especially for users at cell-edge. In known CoMP systems, the feedback
procedure is often designed based on single cell non-cooperative scenarios,
and in
some scenarios additional feedback would be needed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] The present disclosure may be understood, and its numerous objects,
features and advantages obtained, when the following detailed description is
considered in conjunction with the following drawings, in which:
[0006] Figure 1 shows a block diagram of one embodiment of a wireless
network
having a Remote Radio Head (RRH) deployment.
[0007] Figure 2 shows a block diagram of one embodiment of a wireless
network
having a homogeneous network deployment.
[0008] Figure 3 shows a block diagram of procedures for downlink data
transmission between an eNB and a UE according to one embodiment.
[0009] Figures 4A-4C show block diagrams of CSI-RS pattern examples.
[0010] Figure 5 shows a flow chart of a method of transmission block
processing
for downlink shared channel according to one embodiment.
[0011] Figure 6 shows a schematic block diagram of the physical layer of a
wireless device for physical channel processing according to one embodiment.
[0012] Figure 7 shows a block diagram of an example of a CSI-RS
configuration
for four nodes in a cell, each with two antenna ports.
[0013] Figure 8 shows a block diagram of an example of a TP specific CSI-RS
configuration.
[0014] Figure 9 shows a block diagram of an example of a joint transmission
from
multiple TPs with mixed ranks.
[0015] Figure 10 shows a block diagram of an example of beamformed
distributed transmit diversity.
[0016] Figure 11 shows a block diagram of an example of a rank 2 data
transmission with Tx diversity across two TPs, each with two antennas.
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[0017] Figure 12 shows a block diagram of an example of resource allocation
in
separate sub-band transmission modes.
[0018] Figure 13 shows a flow chart of an example of CoMP codeword
splitting
for a single codeword.
[0019] Figure 14 shows a flow chart of an example of transport block
processing
for repeating the output of channel encoder on separate sub-bands.
[0020] Figure 15 shows a block diagram of CSI feedback for closed-loop CoMP
transmission.
[0021] Figure 16 shows a block diagram of an example of sharing of a CSI
configuration between different RRH.
[0022] Figure 17 shows a block diagram of an example of CSI-RS
configuration.
[0023] Figure 18 shows a block diagram of a wireless device according to
one
embodiment.
[0024] Figure 19 shows a wireless-enabled communications environment
including an embodiment of a client node.
[0025] Figure 20 is a simplified block diagram of an exemplary client node
including a digital signal processor (DSP).
[0026] Figure 21 is a simplified block diagram of a software environment
that
may be implemented by a DSP.
DETAILED DESCRIPTION
[0027] An apparatus and method are provided for feedback solutions that
function
in conjunction with CoMP transmissions. The feedback solutions are applicable
to
joint transmission (JT) as well as coordinated scheduling (CS) and coordinated
beamforming (CB). Embodiments of the present disclosure are described herein
in
the context of a wireless network in compliance with LTE standards, including,
but
not limited to, Releases 8, 9, and 10. However, a skilled artisan will
appreciate that
the embodiments can be adapted for networks of other wireless standards.
[0028] More specifically, in one embodiment, the feedback solution can
include
per Transmission Point (TP) Precoding Matrix Indicator (PMI), per TP Rank
Indicator
(RI) and per TP and per codeword Channel Quality Indicator (CQI) feedback as
well
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as per codeword joint CQI feedback. A TP here could refer to an eNB (node B),
a low
power node (LPN) or remote radio head (RRH). In this embodiment, for each
configured sub-band or for a whole (wideband) system bandwidth, a UE feeds
back:
one PMI and one RI for each TP configured, and one non-JT CQI for each TP and
each codeword (derived assuming DL data transmission from the individual TP
with
the corresponding PMI and RI), and/or one JT CQI for each codeword (derived
assuming joint transmission from all the configured TPs with the fed-back PMIs
and
RIs), where the number of codewords is determined by the maximum number of
data
layers across all the TPs. In the case of joint transmission, layers precoded
at and
transmitted from a TP i, indexed by S, (i=0,1,...,NTp-1 ) where NTp is the
number of
TPs in a COMP set configured for the UE, may be predefined such that both the
eNB
and the UE know how to derive S, from reported RIs, configured by the eNB
either
dynamically (e.g., via PDCCH) or semi-statically (e.g., via RRC signalling) so
that a
UE knows the layer assignment for joint CQI calculation, or derived at the UE
and
signalled to the eNB.
[0029] In another embodiment, the feedback solution can include per TP PMI,
per
TP RI, per TP and per codeword CQI feedback and per TP Phase feedback as well
as
per codeword joint CQI feedback. This embodiment is similar to the first
embodiment except that a relative phase offset term for each TP is also fed
back and
the common (JT) CQI that is fed-back is derived assuming that the relative
phase
offsets are corrected by the participating TPs. Thus, for each configured sub-
band or
for the whole (wideband) system bandwidth, a UE calculates and feeds back: a
PMI
and an RI per TP assuming joint transmission, and a relative phase offset term
per TP
per data layer assuming a common reference point such that the precoded
signals
from all the TPs with the feedback PMIs would be constructively added at the
UE
receiver, and a non-JT CQI per codeword per TP assuming non-joint (per TP)
data
transmission with the feedback PMI and RI, and /or a common CQI per codeword
assuming joint transmission with the fed back PMIs, RIs and correction for the
relative phase offset terms, where the number of codewords is determined by
the
maximum number of data layers across all the TPs. Layer mapping in each TP in
the
case of joint transmission may be: predefined such that both the eNB and the
UE
know how to derive S, from RIs and probably other channel state information
(CSI),
configured by eNB either dynamically (e.g. via PDCCH) or semi-statically (e.g.
via
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RRC signalling) so that a UE knows the layer assignment for joint CQI
calculation,
and/or derived at the UE and signalled from UE to eNB.
[0030] In another embodiment, the feedback solution can include per TP PMI
and
per TP CQI feedback as well as joint CQI feedback where a UE feeds back a
single
common RI for all TPs instead of per TP RI.
[0031] In another embodiment, the feedback solution can include per TP PMI,
per
TP RI, and per TP CQI feedback for all the TPs in a COMP set and joint CQI
feedback for partial TPs in the COMP set. This embodiment is similar to the
second
and third embodiments except that a UE may indicate to the eNB that some of
the TPs
in the COMP set may not be good for joint transmission and are excluded from
the
CQI calculation for joint transmission. One of the following methods can be
used:
use per TP CQI = 0, which is already defined in the specification, add a state
corresponding to no transmission, e.g., rank=0, to the rank index table and
send that
index as the per TP RI, and/or add an all zero entry to each of the codebooks
and
feedback the per TP RI corresponding to rank=0 and/or the per TP PMI
corresponding
to all zero entry in a codebook when this situation occurs.
[0032] In another embodiment, the feedback solution can include independent
per
TP sub-band PMI, RI and/or CQI feedback. These CSI parameters are calculated
assuming single-point transmission from the corresponding TP on that sub-band.
A
UE may feedback PMI/RI/CQI for a subset of the sub-bands, where the subset may
be
the same or different for each TP. Some examples of subset selection methods
include: for each sub-band the CSI of a TP providing the highest throughput is
reported, for each TP, the CSI of a certain number of sub-bands is reported.
These
sub-bands could include those with good enough channel conditions or simply
the
best M sub-bands, where M is pre-defined and known by both transmitter and the
receiver.
[0033] An apparatus and method are also provided for transmission schemes
for
utilizing feedback solutions that functions in conjunction with CoMP
transmissions.
[0034] More specifically, in one embodiment the transmission schemes for
enabling feedback solutions can provide for joint transmission over the same
sub-
bands from multiple TPs with the same codewords. In this embodiment, TPs
transmit
the same data layers to a UE on the same time/frequency resources. Each data
layer is
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precoded at each TP using a precoding vector that is part of a precoding
matrix
corresponding to the fed-back PMI from the UE. Each data layer k, on TP i may
be
multiplied by eik , where Oik is a phase value that is either fed back from
the UE or is
set as zero otherwise. If the channel's rank from a TP is smaller than the
total number
of data layers transmitted to the UE, a subset of data layers are transmitted
by the TP.
The subset is assumed to be known by both the eNB controlling the TP and the
UE.
The layer indices could be signalled to the UE through either RRC or PDCCH
[0035] In another embodiment, the transmission scheme for feedback
solutions
can provide joint transmission over the same sub-bands from multiple TPs with
different codewords. In this embodiment, different data layers may be
transmitted
from different TPs on the same time/frequency resources and to the same UE.
The
data layers transmitted from one TP may be associated with codewords that are
different from the codewords transmitted on other TPs, namely TP-specific
codewords. Hence, more than two codewords may be sent to the same UE on a
single
radio carrier. Additionally, a TP may be assigned a rank=0 transmission, i.e.,
no data
transmission at all from the TP. This assignment is signalled to the UE.
[0036] In another embodiment, the transmission scheme for enabling feedback
solutions can provide transmit diversity across TPs. In this embodiment, when
two
TPs are involved in a joint data transmission to a UE, the two TPs can be
considered
as two or four virtual antenna ports after precoding with their corresponding
precoding matrix indicated by the fed-back PMI. In the case of rank 1
transmission, a
single codeword is encoded by Alamouti (such as Space-Frequency Block Coding
(SFBC) ) coding to generate two layers, each is transmitted from one TP after
undergoing separate precoding at each TP. In the case of rank 2 transmission
with
two codewords, each codeword is encoded by Alamouti (SFBC) coding to generate
two layers, each is transmitted from one TP after undergoing separate
precoding at
each TP. Alternatively , when two TPs each have either one or two antennas,
the
release 8 2-port or 4-port Tx diversity scheme is used over the two TPs
without
precoding. In this alternative, TP specific RS ports is defined or UE-specific
reference signal (DM-RS) ports as defined in releases 9 and 10 are reused for
channel
estimation for demodulation.
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[0037] In another embodiment, the transmission scheme for enabling feedback
solutions can provide open-loop spatial multiplexing CoMP transmission. In
this
embodiment, open-loop transmission is applied across the antenna ports of
multiple
TPs. Each TP transmits the same or a different data stream and no PMI feedback
is
required. When each TP has more than one antenna port, open-loop precoding is
performed at each TP. The precoding vectors or matrices at each TP are
predefined
and thus no PMI feedback is required. In this embodiment, DM-RS may be used
for
data transmission, and the UEs do not need to know the precoding vectors or
matrices.
[0038] In another embodiment, the transmission scheme for utilizing
feedback
solutions can provide joint data transmission over different sub-bands from
multiple
TPs. In this embodiment, joint data transmission is performed on separate (non-
overlapping) sub-bands from multiple TPs with at least one of the following
options:
Different TPs transmit different segments of a codeword on separate sub-bands
with
single MCS across separate sub-band, or different TPs use the output of the
same
channel forward error correction encoder and apply rate matching separately to
achieve different MCS across separate sub-bands, then, each TP transmits its
portion
of the codeword on a separate sub-band from other TPs, or each TP has a
separate TB
on which it applies channel coding, the codewords of different TPs are then
transmitted on separate sub-bands.
[0039] An apparatus and method are also provided for configuring feedback
and
transmission schemes that function in conjunction with CoMP transmissions.
[0040] More specifically, in one embodiment the configuring feedback and
transmission schemes that function in conjunction with CoMP transmissions
provides
for configuration of feedback modes of operation. In certain embodiments, the
solutions for configuring a feedback reporting mode for a closed loop CoMP
transmission includes supporting feedback of common rank (i.e., one rank for
all TP)
or separate rank for each TP (the separate rank for each TP may be jointly
coded and
fed-back together in the same rank report (RI)). In certain embodiments, for
each TP,
a separate CQI/PMI reports as defined in release 8 to release 10 is fed back
to the
eNB, the CQI feedback in such reports assumes a single TP transmission and is
derived the same way as defined in previous releases. In certain embodiments,
the
CQI/PMI reports for each TP are transmitted in either PUCCH or PUSCH. If
transmitted in PUCCH (e.g., as a periodic report), different reports for
different TP
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are transmitted in different subframes in a Time Division Multiplexed (TDM)
manner.
If transmitted in PUSCH (e.g., as an aperiodic report), all reports for
different TP are
multiplexed together. In certain embodiments, in addition to the above
reports, CQI
reports are configured which feedback a jointly derived CQI for each codeword
assuming that the same layers of data are transmitted from each TP. Such
reports are
transmitted on PUCCH as periodic reporting and multiplexed with other CQI/PMI
reports in TDM manner or multiplexed with other CQI/PMI reports and
transmitted
on PUSCH as aperiodic reporting.
[0041] More specifically, the solutions for configuring a feedback mode for
a
closed loop CoMP transmission includes extending feedback on PUCCH and/or
PUSCH for closed-loop transmission via the release 8 feedback modes 1-1, 2-1
for
PUCCH, and modes 3-1, 1-2 and 2-2 for PUSCH. In these modes, for each TP, the
same types of feedback reports as defined in release 8 are used. Additionally,
joint
CQI reports are derived and fed-back. In certain embodiments, for selected sub-
band
reporting, the selection of the best-M sub-bands is based on joint CQI from
multiple
TPs rather than individual CQI for each TP. In these embodiments, the UE then
derives and feeds back separate CQI/PMI reporting for each TP based on
selected
sub-bands and assumes individual transmission from each TP. In certain of
these
embodiments, the UE could in addition derive and feedback joint CQIs for each
selected sub-band by assuming joint transmission from all participating TPs.
[0042] In another embodiment, the configuring feedback and transmission
schemes that function in conjunction with CoMP transmissions provide for
configuration of transmission modes of operation. In certain embodiments, the
solutions for configuring a transmission mode for a CoMP transmission include
configuring a closed-loop spatial multiplexing CoMP transmission mode. The
transmission mode supports separate CQI/PMI reporting for each TP. In
addition, a
joint CQI feedback is configured. Dynamic switching between CoMP and non-CoMP
transmission is supported by this mode of operation. In certain embodiments,
configuring an open-loop spatial multiplexing CoMP transmission mode, which
does
not need PMI feedback from the UE. In this embodiment, optionally, pre-defined
or
eNB determined precoding vectors are applied at the TPs. In certain
embodiments,
Configuring both closed-loop and open-loop spatial multiplexing CoMP
transmissions
is included in one transmission mode (i.e., a Spatial multiplexing CoMP
transmission
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mode). Which transmission (i.e., closed-loop or open-loop) is in effect is
made to be
transparent to the UE. The UE needs only be configured with different feedback
modes to achieve the switch between them. For example, if the UE is configured
with
CQI only (no PMI) feedback, open-loop transmission is used, while if the UE is
configured with PMI/CQI feedback, closed-loop transmission is used. In certain
embodiments, transmit diversity with or without precoding is configured for
two TPs.
Alamouti types of encoding are applied to generate pairs of coded symbols
which are
transmitted from each TP. CQI calculation at the UE for feedback assumes that
Alamouti coding is used.
[0043] An apparatus and method are also provided for a CSI-RS solution that
functions in conjunction with CoMP transmissions. This solution considers a
method
of CSI-RS multiplexing in a cell with a macro-eNB and multiple low power nodes
(LPNs) sharing the same cell ID. Two CSI-RS configurations can be used, one
for
the macro-eNB and the other for all the LPNs. Each LPN transmits the CSI-RS
over
different sub-bands and the system bandwidth or bandwidth of operation is
covered
by CSI-RS from all the LPNs. The sub-band on which CSI-RS is transmitted for
each
LPN hops across the whole system bandwidth over time. The hopping pattern of
CRS-RS for each LPN could follow the same cycle but with different sub-band
offset.
The CSI-RS for the macro-eNB is transmitted separately across the whole system
bandwidth.
[0044] Various illustrative embodiments of the present disclosure will now
be
described in detail with reference to the accompanying figures. While various
details
are set forth in the following description, it will be appreciated that the
present
disclosure may be practiced without these specific details, and that numerous
implementation-specific decisions may be made to the invention described
herein to
achieve the inventor's specific goals, such as compliance with process
technology or
design-related constraints, which will vary from one implementation to
another.
While such a development effort might be complex and time-consuming, it would
nevertheless be a routine undertaking for those of skill in the art having the
benefit of
this disclosure. For example, selected aspects are shown in block diagram and
flowchart form, rather than in detail, to avoid limiting or obscuring the
present
disclosure. In addition, some portions of the detailed descriptions provided
herein are
presented in terms of algorithms or operations on data within a computer
memory.
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Such descriptions and representations are used by those skilled in the art to
describe
and convey the substance of their work to others skilled in the art.
[0045] In a network of LTE standards, CSI Reference Signals (CSI-RS) can be
transmitted in certain subframes as a reference signal. Assuming the Channel
State
Information ¨ Reference Signal (CSI-RS) is designed such that a UE can measure
the
channel of a macro-eNB and each Remote Radio Head (RRH) separately, it is
desirable to enable efficient transmission schemes. In such transmission
schemes, it is
desirable to avoid excessive feedback overhead. Also, it is helpful to reuse
the
components or structure of the existing feedback mechanisms as much as
possible to
minimize the impacts to both the system and the UE. For example, a Precoding
Matrix Indicator (PMI) (which is used by the UE to feedback to the eNB its
preferred
precoding vector or matrix) may be confined to be selected from existing
codebooks.
Accordingly, it is desirable to provide a feedback mechanism that functions in
conjunction with CoMP transmission methods.
[0046] Additionally, the performance of a CoMP operation strongly depends
on
the transmission scheme. Hence, it is important to coordinate signal
processing at
different Transmission Points (TPs) to form an efficient transmission that can
utilize
the benefits of CoMP. This coordination can be in the form of coordinated
beamforming (CB) and/or coordinated scheduling (CS), where each UE can receive
data only from a single TP at a time; however, the PMI and/or time/frequency
resources are coordinated between the nodes in the CoMP set to minimize or
avoid
interference caused to other UEs. An alternative method of coordination could
be
realized through joint transmission (JT), where the UE receives data from
multiple
TPs at the same time.
[0047] In release 10 of the 3GPP specification, CSI-RS was introduced for
the UE
to measure CSI for a downlink transmission. The signalling overheads of CSI-RS
from the eNB to the UE increase as the number of transmit antennas involved in
the
Multiple Input and Multiple Output (MIMO) transmission is increased. To
control
this signalling overhead and yet support up to 8-tx transmission, CSI-RS are
not
transmitted in every subframe and thus the CSI-RS are more sparse in the time
domain compared with Re1-8 common (or cell-specific) RS (CRS). In release 10,
each UE is required to measure and report CSI based on a single CSI-RS
configuration. In release 11 of the 3GPP specification study phase of CoMP
scenario
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4, all the low power nodes (LPNs) such as RRHs within a macro-cell coverage
area
and the macro eNB itself share the same cell ID. In this case, the UE may not
be
informed directly of the presence of the RRHs, but only with the CSI-RS ports
associated with each RRH. Because the number of RRHs in a cell could be
relatively
large, it is desirable that the CSI-RS design and configuration be simple and
flexible.
It is also desirable that the CSI-RS design and configuration be transparent
to release
type UEs for backwards compatibility purposes. It is also desirable that the
complexity increase at the UE be kept low.
[0048] In a system deploying CoMP operation, a set of
transmissioiVreception
nodes that cooperate with each other to serve one or multiple UEs form a CoMP
set.
The nodes in a CoMP set may be eNBs and/or low power nodes (LPNs) such as
remote radio heads (RRHs). The LPNs can include, but are not limited to, a
microcell, a picocell, a femtocell, and the like.
[0049] Figure 1 shows an example of a CoMP deployment with one macro-eNB
and six RRHs, where the macro-eNB is located at the center of a cell while the
six
RRHs are located at the cell edge. The nodes in a CoMP set are assumed to be
connected through backhaul, e.g. by optical fibre.
[0050] The cooperating nodes can send and receive either digitized baseband
signals or radio frequency (RF) signals through the backhaul connections. In
some
implementations, instead of point to point connections between all nodes, the
nodes
can be all connected to a single central entity. This central entity can be,
for example,
an eNB or a central processing center. For exemplative purposes, the backhaul
connections are characterized by zero latency and infinite capacity. To
simplify
discussion, a RRH or the macro-eNB are also referred to as a transmission
point (TP).
[0051] Four different deployment scenarios have been defined for the study
of
CoMP. These four scenarios are categorized into homogeneous and heterogeneous
deployments. More specifically, for homogeneous deployments, a first scenario
describes a homogeneous network with intra-site CoMP and a second scenario
describes homogeneous network with high Tx power RRHs (inter-site CoMP). For
heterogeneous deployments, a third scenario describes a heterogeneous network
with
low power RRHs within the macrocell coverage where the transmissioiVreception
points created by the RRHs have cell IDs different from the macro cell. A
fourth
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scenario describes a heterogeneous network with low power RRHs within the
macrocell coverage where the transmission/reception points created by the RRHs
have the same cell IDs as the macro cell.
[0052] In a
homogeneous network deployment, macro-cells are generally formed
by placing eNBs uniformly in a geographical area. Each of the cells is served
by an
eNB with the same or similar transmit power and thus has the same or similar
size.
An example is shown in Figure 2, where total of 21 cells are deployed with six
cell
sites. Each site includes three eNBs, one for each cell. Cell tower
is normally
deployed in each site to provide a large coverage area and high transmit power
is
typically used.
[0053] While in a
heterogeneous deployment, low power nodes are placed
throughout a macro-cell layout. An example is shown in Figure 1, where the
RRHs
could be low power nodes.
[0054] The
described embodiments in this application apply to all these four
scenarios unless otherwise specified. Also, the described embodiments are
based on
an LTE system, although the concepts are equally applicable to other wireless
systems
as well.
[0055] To enable
coherent reception of downlink data signals and to facilitate
measurements which may be used to enable modulation and coding rate
assignment,
systems such as LTE utilise reference signals (RS) which are transmitted by
the eNB
in addition to the data signals. In MIMO systems, different RS may be
transmitted
from different transmit antennas. Receivers in the system (such as a UE)
commonly
process the received RS to determine Channel State Information (CSI) for a
given
moment in time. CSI may be obtained for multiple transmit/receive antenna
pairs
(i.e., the individual channels that collectively constitute a MIMO channel).
The CSI
information obtained by the receiver is used to enable or improve reception of
the
downlink data signals.
[0056] Different
types of RS are defined in the LTE system. More specifically,
Cell-Specific (Common) Reference Signals (CRS) are RS that are regularly
transmitted throughout the cell and which are available to all UEs. CRS are
not
precoded, hence if a precoded data signal is transmitted to a UE, the UE
receiver
requires knowledge of both the CSI (obtained from the non-precoded CRS) and
the
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precoding vector or matrix that was employed at the eNB, to form an estimate
of the
composite (precoded) channel through which the data signal has passed (this
being
necessary to correctly demodulate the data signal). This is commonly referred
to as
codebook-based precoding, as the selected precoding vector or matrix typically
is one
from a predefined set of possible precoding vectors or matrices (a codebook).
Antenna ports 0 to 3 use CRS in the LTE system. Additionally, UE-Specific
(Dedicated) Reference Signals (DRS) are RS that are embedded along with data
intended for a specific recipient UE. DRS are generally precoded using the
same
precoding vector or matrix as is applied to the data signal (the precoding is
usually
arranged to optimise a quality of reception at the intended UE). Hence, the UE
receiver does not require knowledge of the precoding vector or matrix that has
been
applied at the transmitter ¨ rather it simply determines a composite CSI
(including the
effects of both the precoding and the propagation channel) from DRS and uses
this
composite CSI to demodulate the precoded data signal. Antenna ports 5, and 7
through 14 use DRS in the LTE system.
[0057] Additionally, CSI Reference Signals (CSI-RS) are RS that are
transmitted
in certain preconfigured subframes and are intended for all Rd-10 UEs in a
cell. CSI-
RS are similar to CRS except that: they are used for CSI estimation only for a
Rd-10
UE and are not used for data demodulation at a UE, they are not transmitted on
every
subframe, and there are multiple configuration options available, the
configuration of
CSI-RS in a cell is independent of the cell ID.
[0058] An example of a transmission scheme utilising CSI-RS is shown in
Figure
3. The figure shows a simplified block diagram of eNB-UE procedures for
dynamic
DL data scheduling and transmission in LTE-A (Rel-10) using transmission mode
9
(TM 9). DL data transmission in other transmission modes would be similar. In
LTE,
9 DL transmission modes have been defined, and each supports certain
transmission
schemes such as single antenna transmission, multiple antenna transmission
with
transmit diversity, open-loop or closed- loop MIIVIO, multi-user MIMO (MU-
MIMO),
etc. A complete list of DL transmission modes in LTE is shown in Table 1
below.
TM1 to TM7 are defined in Re1-8. TM8 was introduced in Re1-9 to support DL
dual
layer beamforming, and TM9 was introduced in Rd-10 to support up to eight
layers
of MEMO transmission with up to eight transmit antennas.
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Table 1: DL transmission modes and supported DL transmission schemes for
dynamically scheduled UE specific PDSCH data in LTE
Transmission Supported DL Re1-8 Re1-9 Rd-10 RS for DL RS for
mode transmission scheme CSI PDSCH
measurement demodulation
Mode 1 Single antenna, port 0 yes Yes yes CRS CRS
Mode 2 Transmit diversity yes Yes yes
Mode 3 Open-loop MIMO yes Yes yes
Transmit diversity yes Yes yes
Mode 4 Closed-loop MIMO yes Yes yes
Transmit diversity yes Yes yes
Mode 5 MU-MIMO yes Yes yes
Transmit diversity yes Yes yes
Mode 6 Closed-loop MIMO yes Yes yes
with a single
transmission layer
Transmit diversity yes Yes yes
Mode 7 Single layer yes Yes yes CRS DRS
beamforming
Transmit diversity or yes Yes yes CRS CRS
single antenna port
Mode 8 Dual layer Yes yes CRS DRS
beamforming
Transmit diversity or Yes yes CRS CRS
single antenna port
Mode 9 Up to 8 layer closed- yes CSI-RS DRS
loop MIMO
transmission
Transmit diversity or yes CSI-RS CRS
single antenna port
transmission
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[0059] As shown in Figure 3, a plurality of steps can be performed by the
eNB
and the UE. More specifically, a CSI-RS Configuration step 310 is performed.
In
release 10, a set of RS, namely CSI-RS symbols, are defined. CSI-RS are used
for
channel measurements and for deriving feedback on the quality and spatial
properties
of the channel(s) as needed. It is expected that CSI-RS will be the main
reference
signals used for CoMP operation in subsequent releases of LTE. The feedback
derived by the UE from CSI-RS can be used for different transmission schemes
such
as single-cell single and multi-user MEMO, as well as coordinated multi-cell
transmission.
[0060] The configuration of CSI-RS is cell specific and includes parameters
that
define the pattern, periodicity, subframe offset, and number of CSI-RS ports.
CSI-RS
patterns adopt a base pattern with length-2 time domain Orthogonal Cover Codes
(OCC) for each pair of antenna ports. The patterns have a nested structure,
where the
pattern used for a smaller number of CSI-RS ports is a subset of the pattern
used for a
larger number of CSI-RS ports. Multiple patterns/configurations are available
for the
network to provide varying pattern reuse factor across cells or TPs. The
configuration
parameters of CSI-RS are explicitly signalled via higher layers (via Radio
Resource
Control ¨ RRC ¨ signalling) within each cell. An example of a CSI-RS
configuration
for the normal cyclic prefix (CP) duration is shown in Figure 4.
[0061] Next, a Channel Estimation step 312 is performed. Based on the
received
signal on the CSI-RS resources, the UE estimates the DL channel on the
corresponding resource elements.
[0062] Next, a CSI Calculation step 314 is performed. The UE measures and
reports channel state information (CSI) to the eNB for efficient data
transmission. The
CSI feedback may include parameters such as a channel quality indicator (CQI),
a
precoding matrix indicator (PMI), a precoding type indicator (PTI), and a rank
indication (RI). Depending on the feedback mode, all or some of these
parameters are
included in CSI feedback.
[0063] CSI feedback could be wideband or sub-band. In wideband CSI
feedback,
a single value of each CSI parameter is calculated and reported for the whole
bandwidth. In sub-band CSI, the whole bandwidth of the carrier is divided into
sub-
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bands (with a configurable size) and for each sub-band a set of CSI parameters
is
calculated and reported to the eNB.
[0064] The CSI feedback parameters derived by the UE can form part of the
uplink control information (UCI) that is transmitted by the UE on either a
physical
uplink control channel (PUCCH) or a physical uplink shared channel (PUSCH).
[0065] Next, a scheduler step 316 and a DL grant step 318 are performed.
The
scheduler decides which time/frequency resources of a Physical Downlink Shared
Channel (PDSCH) are assigned for DL transmission to the UE. The time/frequency
resources are expressed in terms of the assigned Resource Blocks (RB), with
one RB
comprising 12 sub-carriers of frequency resource during one 0.5 ms slot of
time
resource. This assignment information along with other transmission
parameters,
form the DL grant are transmitted as downlink control information (DCI) on the
physical downlink control channel (PDCCH) to the UE at step 320. This
information
is detected and recorded by the UE, and used for detection of the data sent on
PDSCH
at step 322.
[0066] Next, a transport block processing step 324 is performed. Data
arrives
from a higher layer in the form of transport blocks (TBs). In current releases
of LTE,
a maximum of two TBs are transmitted in each transmission time interval (TTI).
Each
TB is encoded into a codeword in a few steps as shown in Figure 5. First, a
Cyclic
Redundancy Check field (CRC) is attached to the TB. If the size of the TB is
larger
than a certain value, code block segmentation is applied to divide the TB into
smaller
blocks termed code blocks. Channel coding is applied on each code block
separately.
Rate matching is applied based on the modulation and coding scheme (MCS)
assigned
to the UE. Finally, the rate matched coded bits are concatenated to form a
codeword.
[0067] Next, a physical channel processing step 326 is performed. The
codeword
formed by the coding unit is converted into OFDM symbols to be transmitted on
the
DL channel. Figure 6 shows the steps involved in this process. Each codeword
is first
scrambled by a cell-specific scrambling sequence. The scrambled bits are then
modulated to form modulation symbols. The modulation symbols from all
codewords
are mapped to layers, where the number of layers (or transmit rank) is
indicated in the
DL grant carried in the PDCCH. Subsequently, the precoding is applied to the
data
layers to form the signals for each antenna port. The output of the precoder
is mapped
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to resource elements in the frequency domain and then the OFDM signal in time
domain is generated and transmitted over each antenna port. A Resource Element
(RE) is a minimum unit of time/frequency resource, defined in the LTE system
as one
OPDM symbol duration in time and one sub-carrier in frequency.
[0068] The block diagram of Figure 3 describes the procedures for downlink
data
transmission in a non-CoMP transmission. For CoMP transmission, some of these
procedural components may need to be modified to fully utilize the potential
of
cooperative communications.
[0069] There are a plurality of feedback and transmission methods for multi-
point
operation. One such method feeds back a joint CSI. In this method, multiple
TPs are
considered together as a virtual single TP. Denoting the channel matrix from
TP i to
the UE by Hi, the composite channel from this virtual single TP to the UE is
equal to
H= [H1 = = = Hnl.
[0070] Based on 11,, one set of CSI (e.g., PMI, CQI, and RI) are calculated
and
fed back to the eNB. This scenario is suited for joint transmission (JT) of
the same
data from all cooperating TPs. A benefit of this method is that the same
feedback
modes as used in current/legacy systems can be reused, yet the advantages of
multiple
point transmission can still be utilized.
[0071] One issue of this feedback method is that the existing codebooks are
only
designed for up to eight antenna ports, therefore, if the total number of
antenna ports
from all the TPs involved in a JT is larger than eight, a new codebook may be
required. Another issue is that the transmit power of the multiple TPs, and
consequently the signal strengths received from them at the UE side, may not
be the
same, whereas known codebooks are designed assuming the same power level for
all
antenna ports. Hence, known codebooks may not be efficient for use in joint
transmission in heterogeneous networks where the transmit powers from each TP
may
not be the same, thus a new design may be desirable. Another issue is that
known
codebooks are often designed assuming that all antennas are co-located on the
same
TP and therefore close to each other; with more distributed antennas on
different TP,
the codebook may need to be modified to accommodate different antenna
correlations.
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[0072] Another method feeds back separate rank-1 PMI, common CQI and inter-
TP phase information. This method feeds back separate rank-1 PMIs for each TP
and
allows the TPs to each transmit the same data using their own PMI (and using a
common CQI). With this method, each TP can individually apply beamforming to
the
data it transmits; however, due to uncontrolled phase differences between TPs,
the
signals from the different TPs may add with random phases, thus limiting an
overall
beamforming gain. One solution to this issue is to feedback some phase
information
about channels from each of the TPs and to utilize such information at the TPs
during
beamforming operation in an attempt to achieve constructive phase alignment at
the
UE, thereby helping to achieve higher overall beamforming gains.
[0073] In certain known methods, this phase feedback method for rank-1
transmission is used with two TPs. The PMI for each TP is obtained from its
channel
matrix and a phase difference 0 is calculated such that when the transmission
phase at
TP#2 is compensated by this value, the received signals from both TPs add
coherently
at the UE side. In mathematical notation, this transmission method is
described as
Y = efell21w2)x+n
where y denotes the received signal vector at the UE's receive antennas, Hil
and 1121
represent the channel matrices between TPs 1 and 2 and the UE respectively, w1
and
w2 represent the precoding vectors applied at TPs 1 and 2 respectively, and n
is a
vector of additive thermal noise at the UE's receiver.
[0074] In another solution as opposed to the individual (per-TP) PMI
calculations,
the PMI calculation is carried out jointly. In this joint calculation
approach, the PMIs
are assumed to be sub-vectors of a single precoding vector calculated based on
the
composite channel H. In other words, denoting the right singular vector of H
by v,
then v is quantized as
a2e'e2p2T === anefe.põTIT,
Q(v)= [aiPiT
where Q(.) indicates the quantization operation; pi (i=1,2,...,n) is a m, x/
(m,
=1,2,4,8) precoding vector for TP i chosen from a codebook for m, antenna
ports and
m, is the number of Tx antennas at TP i; a, and 0, are the channel amplitude
and phase
values associated with TP i. Because of the additional amplitude information
and also
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joint calculation of PMIs, more gain is expected with this approach when
compared
with the individual PMI calculation method.
[0075] One issue of the aforementioned methods however is that whilst both
work
for rank-1 transmission, it is not clear how to feedback phase information for
transmission ranks larger than one. Also, in the first method, if the number
of receive
antennas is larger than 1, it is not possible to choose the phase value 0 such
that the
received signals add constructively on all receive antennas.
[0076] Another method feeds back separate per TP PMIs, RIs and CQIs which
are
jointly calculated. In this method, the UE feeds back PMI, RI, and CQI for
each TP
individually, and each TP transmits different data streams to the UE. The
transmission
can be described as
y = H1W1x1 +11
where y denotes the received signal vector at each of the UE's receive
antennas, H,
represents the channel matrix between the transmit antennas of the ith TP and
the UE's
receive antennas, W, represents the precoding matrix applied at the ith TP, x,
is the
data symbol transmitted from the ith TP and n is a vector of additive thermal
noise at
each receive antenna.
[0077] In this method, different data streams are transmitted from
different TPs
and a joint optimization is applied for selecting the per TP PMI, RI, and CQIs
for all
TPs to maximize the overall data throughput by taking into account the
possible
interference between different TPs.
[0078] Another method provides a CSI-RS design. From LTE Release 10
onwards, cell specific CSI-RS have been introduced for UEs to measure and
feedback
DL channel state information (CSI) from a single serving cell (i.e. the cell
that is used
for downlink transmission to the UE). A Rel-10 UE may be configured with
multiple
sets of CSI-RS configurations, one for the serving cell and others for other
neighboring cells. The CSI-RS configuration for the serving cell is typically
indicated
as a non-zero transmission power CSI-RS configuration, while CSI-RS
configurations
for other cells are indicated as CSI-RS with zero transmission power and could
be
used by the UE to measure the channels from other cells (that is, the resource
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elements associated with some CSI-RS are left empty by the serving cell to
facilitate
improved reception of CSI-RS from other cells on those RE at the UE). In Rel-
10, a
UE only measures and feeds back DL CSI based on this non-zero transmission
power
CSI-RS.
[0079] When RRHs are deployed in a cell covered by a macro-eNB and when the
RRHs share the same cell ID as the macro-eNB, a few options for CSI-RS
configuration have been considered. In one scenario, the antennas of the RRHs
are
considered as part of the macro-eNB and thus a single CSI-RS configuration may
be
used where one CSI-RS port is assigned to each of the antenna ports. For
example,
assuming one macro-eNB and three RRHs are deployed in a cell sharing the same
cell
ID and each with two antenna ports, then an 8-port CSI-RS configuration
defined in
Rel-10 can be used in which one CSI-RS is assigned to each of the antenna
ports. As
shown in Figure 7, the Rel-10 CSI-RS configuration #0 with 8 CSI-RS ports can
be
used.
[0080] This configuration however does not work when the total number of
antenna ports (macro eNB + RRHs) exceeds eight because the maximum number of
antenna ports supported in Rel-10 is eight.
[0081] An alternative option is to have a separate CSI-RS configuration for
each
TP. An example is shown in Figure 8. Since for each UE, CSI-RS configurations
are
signalled in a UE specific fashion in Rel-10, the eNB can configure each UE
with a
UE specific CSI-RS configuration(s) for channel estimation and CSI feedback. A
UE
sufficiently close to a TP would typically be configured with the CSI-RS
assigned to
that TP. Different UEs would thus potentially measure on different CSI-RS
resources
depending on the locations of the UEs within the coverage area spanned by the
multiple TPs that share the same cell ID. However it should be noted that in
Rel-10, a
UE only measures and reports a single CSI-RS configuration with non-zero
transmission power. For a UE to measure and report channel feedback for
multiple
TPs, some changes are required beyond Rel-10 to enable CSI feedback for
multiple
TPs. In this case, a large number of configurations may be needed to support a
large
number of TPs in a cell. Moreover the eNB needs to know which TPs cover the UE
to
assign the corresponding CSI-RS configurations to the UE. When a UE moves from
the coverage area of one TP to the coverage area of another TP, a CSI-RS
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reconfiguration for the UE may be needed if the CSI-RS of a new TP is not yet
configured for that UE.
[0082] Accordingly, in one embodiment, a feedback method can provide per
Transmission Point (TP) Precoding Matrix Indicator (PMI), per TP Rank
Indicator
(RI) and per TP Channel Quality Indicator (CQI) feedback as well as joint CQI
feedback.
[0083] In this method, the UE feeds back a PMI, an RI and one or more
CQI(s)
for each associated TP. The PMI and RI are calculated assuming joint data
transmission from multiple TPs (as described below) or calculated separately
for each
TP assuming non-joint transmission, whereas the CQI or CQIs are calculated
assuming data transmission from only the corresponding TP using the feedback
PMI
and RI for the TP. In addition, one or two joint CQI(s) are also fed-back,
depending
on whether the number of codewords is one or two, respectively. This feedback
scheme is used for either per TP data transmission to a UE or joint
transmission of the
same layers of data from multiple TPs.
[0084] In the case of joint data transmission, if the transmission rank of
all TPs is
the same, say equal to R, all TPs transmit the same data vector x with length
R. If the
transmission ranks of various TPs are different, then TP i chooses R, data
layers from
x and transmits this sub-vector, where R, is the number of layers supported by
TP i.
An example of this mixed-rank transmission is shown in Figure 9. In Figure 9,
four
layers of data are to be transmitted using three TPs. TP#1 has four antenna
ports, and
TPs #2 and #3 each have two antenna ports. In this example, precoding at TP#1
is
applied to all data layers xi, x2, x3, x4, whilst precoding at TP #2 is
applied only to
x1,x2, and precoding at TP #3 is applied only to x3, x4.
[0085] An index set Si, where Si c {1, = = = , R}, Si = R1, is defined to
denote the
index of the layers precoded and transmitted by TP i. For more accurate CQI
estimates at a UE, the UE should know the index sets used by all TPs. In
various
embodiments, a plurality of approaches are used to assure the UE and the TPs
use the
same S1:
[0086] More specifically, in one approach, a pre-defined rule is used. With
this
approach, the index sets are determined from rank indices (which is known by
the
eNB and the UE via signalling) and based on a pre-defined rule agreed between
the
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eNB and the UE. For example, the rule could be that each TP i with rank index
R,
chooses Si={1,..., R}.. Another example is to set a rule such that the layers
are
distributed on TPs as evenly as possible. For example, in Figure 9 the
assignment is
done such that each data layer is transmitted exactly from two TPs.
[0087] The rule
may be specified in a standard or may be selected from a few pre-
defined sets and signalled semi-statically. Also, the rule may be based on
some known
cell attribute (such as cell ID) or a CoMP set index. In these approaches,
there is no
need for dynamic signalling of S, and no overhead is incurred (e.g. on the
downlink or
uplink control channel).
[0088] In another
approach, an explicit signalling of S, is used. In this approach,
the index sets are determined by the eNB and signalled either dynamically to
the UE
(e.g. as part of the DCI on PDCCH) or semi-statically (e.g. via RRC
signalling). The
eNB's selection of the Sis may be based on CQIs and other uplink control
information
(UCI) or feedback received from the UE. This method imposes some overhead on
downlink control channel.
[0089] In another
approach, reporting S, on UCI and DCI is used. With this
approach, the index sets are determined by the UE and reported as part of UCI
to the
eNB. Similar to other CSI, the eNB uses the UCI received from the UE to make a
decision on the index sets to be used. This final decision is signalled to the
UE on
PDCCH as part of DCI. This method imposes some signalling overhead (e.g. on
the
uplink control channel and downlink control channel). For signalling Si, one
example
approach is to define a bit map with length R, in which a '1' indicates that
the
corresponding layer shall be used for transmission, and a '0' indicates that
the
corresponding layer shall not be scheduled with transmission.
[0090] In general,
this type of joint transmission can be described as in Equation
(1) below.
y = + n (1)
where x(51) denotes the elements of the data vector x with indices in the set
Si. it is
the channel matrix from TT', to the UE, W, is the precoding matrix or vector
used by
TP i, and n is the additive white Gaussian noise.
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[0091] More
specifically, in certain embodiments, the UE feeds back a per TP
PMI and an RI assuming either joint or non-joint transmission, and CQI(s) for
each
TP assuming non-joint transmission. Also, one joint CQI for each codeword is
fed
back, where the total number of codewords is determined by the maximum number
of
data layers across all TPs.
[0092] In the case
of joint transmission, to better match between the feedback
PMI/RICQI from a UE and the actual channel used for the data transmission, the
layers used at each TP are known by both eNB and the UE to facilitate more
accurate
CQI calculation. The layers used at a TP are indicated by index set, Si. Each
index set
Si includes the index of the data layers to be transmitted from TP i. So that
the
network and the UE have a common understanding on the Si for each TP.
[0093] A rule may
be defined on how to derive Si from RIs. Or some pre-defined
index sets could be specified and signalled to the UE semi-statically for each
TP. Si
may be signalled from eNB to the UE (e.g. via RRC signalling or on downlink
control
channel). A preferred value of Si may be derived at the UE and signalled from
UE to
the eNB on uplink control channel. Based on the suggested Si and other UCI
received
from the UE, the eNB derives the Si that shall be used by TP i and signals it
to the UE
on PDCCH as part of DCI.
[0094] Calculation
of precoding matrices W, and layer indices Si for each TP i can
be performed jointly or independently (as in a single cell paradigm).
[0095] In certain
embodiments, when performing a joint PMI/RI calculation, the
UE determines the PMI/RI for all TPs jointly based on all channel matrices.
Based on
the deployment and application scenario and different performance optimization
criteria, a plurality of approaches may be used.
[0096] In a first
approach, a joint PMI and rank selection is performed based upon
maximizing throughput. In a slow mobility scenario, maximizing the
instantaneous
link throughput may be desirable. To obtain the throughput, as the
optimization
criterion, the Equation (1) described earlier can be rewritten as in Equation
(2):
y = HiWix + n , (2)
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where Wi is a precoding matrix which depends on W, and Si, and is obtained by
starting with an all zero matrix and replacing columns indexed by Si with
corresponding columns of W, . Hence, selecting the PMI/RI/S, for each TP to
maximize the theoretical link throughput can be formulated in Equation (3) as:
( H (3)
Pi ¨ Pi
arg max log
or2 R R,
where, p, denotes the transmit power from TP i and ,o-õ2 denotes receiver
noise power
plus interference (from cells outside of the CoMP set). Note that in the
maximization
above, the search space for R, includes all values in the range
0 min(N, ) =
Rim' for which a codebook is defined, where N is the
number of receive antennas at the UE and M, is the number of transmit antennas
in
TP i. The case R1=0 corresponds to W1=0, i.e. an all-zero precoding matrix.
Also, for
a given R1>0, the search space for W, is the codebook defined for rank R, and
M,
antenna ports. Moreover, the search space for Si is all subsets of = = = ,
max Ri of
size R1.
[0097] Also, the
inclusion of the all-zero precoding matrix allows the UE to
suggest to the eNB the exclusion of a specific TP from the CoMP set in case
the eNB
finds it more beneficial to work with a fewer number of TPs. For example, if
there are
two TPs in the CoMP set and the received signal from one TP is much lower than
the
other TP, it is better to use only one TP for transmission in that case.
[0098] The method
described above for jointly selecting the PMI, RI, and the
layer assignment can be used to increase the throughput in a joint
transmission
scenario, where the PMI of each TP is to be selected from an existing
codebook.
However, this approach may lead to computational complexity at the UE. To
reduce
this complexity, the search spaces may be constrained to smaller sets. One way
for
doing this is to predefine the index sets Si. Hence, the maximization in (3)
will have to
be carried out over PMI and RI only.
[0099]
Accordingly, in certain embodiments, the UE measures all channels from
TPs and jointly determines the PMI, the rank, and the selected layers for each
TP to
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maximize the overall throughput criterion. Such information could be fed back
to the
eNB.
[00100] Also, in certain embodiments, the joint PMI and rank selection may be
based on maximizing diversity. More specifically, in scenarios where the
reliability
of the transmission is prioritised rather than the throughput, increasing the
degree of
transmit diversity is desirable. One approach for joint determination of the
PMIs to
increase the diversity is orthogonalization of the equivalent channels from
each TP.
In this method embodiment, W, is chosen such that HiVV, (i = 1, 2, ...) are
mutually
orthogonal to each other, i.e.
W71-1,11 H = 0, i # j .
[00101] For the above equation to have a solution, it is desirable that N ,
where N is the number of receive antennas and R, is the number of layers
transmitted
from TP i. At the same time, the selection of the Wis should be such that the
theoretical throughput is maximized. In other words, in this PMI selection
method, the
Wis are selected to maximize the theoretical throughput subject to the
orthogonality
condition. With this method, the UE first detects the signal on each of the
directions
HiVVi, and then combines them using a maximum ratio combining (MRC) receiver.
Hence, a diversity gain may be achieved. This is in contrast to the throughput
maximizing approach in which beamforming gain is achieved.
[00102] Accordingly, in certain embodiments, the UE measures all channels from
TPs and jointly determines the PMI for each TP to maximize the orthogonality
among
equivalent channels from the set of TPs. Such information is fed back to the
eNB.
[00103] Also, in certain embodiments, a per TP PMI and RI calculation is
performed. More specifically, the UE calculates the PMI and RI for each TP
independently and in a similar way to the legacy single TP systems. In other
words, as
opposed to the solution where each PMI/RI is determined by considering all
channels
together, in this embodiment, the PMI/RI of each TP is determined solely by
the
channel of the corresponding TP.
[00104] One benefit of this CSI calculation is that it is similar to the CSI
calculation in legacy systems and therefore may be transparent to the UE.
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Additionally, the transmission scheme based on this method uses the power
resources
of all TPs. However, in this approach, because the PMI/RI calculation is
carried out
independently for all TPs, the signals from all TPs are added together at the
UE with
random phases and no inter-TP beamforming gain can be obtained.
[00105] If the index set S, is derived based on a predefined rule, only single
cell
PMI/RI needs to be fed back. . For example, if Si = {1, = = = , R,} , the
transmission can
be described as
y = 1-1,Wix(1 + n
[00106] In an alternative approach, if the signalling of S, is possible on an
uplink
control channel, after deriving single cell PMI and RI, the index sets can be
derived
jointly. This operation can be performed by considering a metric similar to
that of
Equation 3 in which Wi and R, are fixed and maximization is carried out with
respect
to S, only.
[00107] Accordingly, in certain embodiments, the UE calculates and feeds back
PMI and rank separately for each TP, or with a fixed rank as configured by the
eNB,
and UE calculates and feeds back separate PMI with fixed rank for each TP. The
eNB
then transmits the same number of data streams or a portion of streams from
each TP.
[00108] Also, in certain embodiments, a CQI calculation is performed. More
specifically, after obtaining the PMI and RI, the CQI is derived based on the
knowledge of what kind of receiver will be used and the calculation of the
corresponding SNR on each data layer. For example, for an MMSE receiver, the
SNR
on layer k is obtained in Equation (4) as
1 (4)
S/NRk = _ 1
(
1
1+ _____________________________ HH õHeq
2
_ kk
whereHeq =1 is the equivalent channel observed by the UE,.
R
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[00109] For the CQI calculation of the ith TP for per TP data transmission,
Hel = H1 W1 should be used in equation (4).
[00110] Alternately, in another embodiment, a feedback method provides
Precoding Matrix Indicator (PMI), Rank Indicator (RI) and Channel Quality
Indicator
(CQI) feedback for each TP as well as common CQI and phase differences.
[00111] As discussed above, for the feedback of separate PMIs/RIs, these
parameters can be calculated either separately or jointly. With the separate
calculation
method, little or no inter-TP diversity or beamforming gain can be achieved.
Joint
calculation, on the other hand, can provide inter-TP beamforming gain or
diversity
gain. However, because the precoding matrices are quantized, part of the
potential
gain cannot be achieved. One solution is to expand the codebook to obtain
finer
granularity for the precoding matrices. However, this method could require
design of
a new codebook which may not be desirable. Another approach is to re-use
existing
codebooks, but also feedback some extra channel-dependent information to
better
match the transmission to the channel state. More specifically, this
additional
information can comprise certain quantized phase values.
[00112] In this embodiment, to help the transmitters to form their signals
such that
their signals are combined coherently at the receiver, the UE calculates and
feeds back
a measure of the phase difference between the received signals of all TPs with
respect
to a reference TP, which is determined based on a pre-defined rule (e.g. the
eNB in a
single cell ID scenario could be the reference TP), or based on cell ID (in a
multiple
cell ID scenario). Also, the phase values can be relative without the eNB and
the UE
agreeing on a specific reference point. As a result, TP i can add a phase
correction Oik
to its data layer k. Considering a general case of mixed rank transmission,
the
transmission can be described in Equation (5) as:
y = HiWielix(S) + n
= A:0,x + n (5)
R(
= eikHik Xk n
k=1
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where 01 = diag(ej " ) is the phase correction diagonal matrix for TP
i, R,
is the transmission rank from TP i (i = 1,2,..., n and k= 1,2, ..., O is
the phase
correction for layer k from TP i,iv-ik is the k-th column of the precoding
matrix W, ,
and W, is a precoding matrix which depends on W, and Si, and is obtained by
starting
with an all-zero matrix and replacing columns indexed by Si with corresponding
columns of W,. 40- , is obtained in the same way from 0 . If the phases are
measured
with respect to a reference TP, the phase matrix of the reference TP is an
identity
matrix. Hence, if the size of the CoMP set is AT,, then AT,-1 quantized phase
matrices
are fed back. If a reference TP is not defined, for example when the CoMP set
dynamically changes, then for each TP one phase matrix should be reported.
[00113] The selection of the precoding matrices W is such that, for each layer
k,
v ik are as aligned as possible in the vector space. Consequently, phase
corrections
01k are chosen such that the received signal vectors of each data layer are
added
constructively at the receiver. If throughput maximization is considered as
the
selection criterion, then selection of W1, Ri, Si, and 0 , can be described in
Equation
(6) as
( VI (6)
1 Pi P11117Viii
1W S i,(1) = arg max log2 I ¨
o-n
where 0, are chosen from a set of quantized phase matrices.
[00114] If the number of receive antennas at the UE is one, and thus the
number of
layers must be one, then the above joint calculation of Wis and 0, s, i.e.
throughput
maximization, is decoupled for different TPs. Also for a TP i, W, and 0, can
be
obtained sequentially. To see this, note that in the single receive antenna
case, the
throughput maximization is equivalent to
2
max IllTieM1H,W,
w,E13,0,1
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where B refers to a codebook. Each term HiWi can be maximized separately from
other terms, i.e. W, only depends on H. Since W, is chosen from the codebook,
1-1,W, with the best W, generally being a complex number, i.e. with both a
magnitude and a phase. Subsequently, the phases 01 should be chosen such that
all
complex numbers ei0g11,W, (i= 1,2,...) have the same phase.
[00115] After obtaining Wi, Ri, Si, and (1) i , the common CQI can be derived
by
li Pi ¨
calculating the SNR on each layer from (4), where H el =
[00116] Accordingly, in certain embodiments, in addition to PMI/RI/CQI
feedback, a UE may feedback one phase value per TP per data layer.
[00117] Alternately, in another embodiment, a feedback method provides
Precoding Matrix Indicator (PMI) and Channel Quality Indicator (CQI) feedback
for
each TP as well as common RI and CQI. More specifically, in this embodiment, a
PMI assuming joint transmission and CQI(s) assuming non-joint transmission are
fed
back for each TP. However, a common RI and a common CQI per codeword for all
TPs (both derived assuming joint transmission) are fed back to the eNB.
Because of
reduced RI feedback, this method has relatively smaller feedback overhead
compared
to the method which provides a per-TP RI. Using common RI for multiple TP also
leads to a more balanced transmission across different layers. For simplicity,
the
common RI can be chosen based on the minimum rank that all TPs can support.
[00118] Because the RI is the same for all TPs, this feedback mechanism is
suitable
to support a combination of codebook-based precoding and transmit diversity
schemes. To be more specific, an Alamouti code can be applied to single layer
data to
generate two layers of coded data, one for each TP. The data at each TP is
then
precoded using the feedback PMI for the TP.
[00119] Accordingly, in certain embodiments, the UE measures all channels from
the TPs and determines a common rank for joint transmission from all TPs and
calculates separate PMI and CQI for each TP and joint CQI, one for each
codeword.
The common rank is obtained jointly or by simply selecting the smallest rank
of those
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derived for the plurality of separate channels from each TP. Such information
is then
fed back to the eNB.
[00120] Alternately, in another embodiment, a feedback method provides
Precoding Matrix Indicator (PMI), Rank Indicator (RI), and Channel Quality
Indicator
(CQI) feedback for each TP with a Rank 0 included. Having separate RI reports
for
different TPs means that different TPs may transmit with different ranks.
Depending
on the channel matrices of the TPs, in some situations, the UE may choose to
receive
all data layers that it can handle, from a single TP or from a subset of the
associated
TPs. In other words, for some realizations of the fading channel, there may be
some
TPs from which the UE does not prefer to receive data. In this case, the UE
assigns an
RI corresponding to rank 0 to such TPs. Alternatively, CQI index 0 could be
used for
this purpose or other signalling methods could be considered.
[00121] Accordingly, in certain embodiments, the UE feeds back separate PMI,
RI,
and CQI for each TP, where the number of CQIs for each TP is determined by the
corresponding RI. The feedback also includes the indication that the UE
prefers not to
receive transmission from a particular TP or TPs. To indicate to eNB that the
UE
does not prefer to receive transmission from a particular TP, one of a
plurality of
methods can be used. More specifically, in one method, the UE can use CQI
index 0,
which is already defined in the specification to indicate CQI out of range.
Alternately, the UE can add a state corresponding to no transmission, i.e.,
rank-0, to
the rank index table and send that index as the RI. Alternately, the UE can
add an all-
zero PMI to the codebooks and feedback the corresponding RI and the all zero
PMI
when this situation occurs. Alternately, the communications with the UE can
include
a bit to indicate if a TP is not preferred by the UE. Alternately, the UE
could signal
this semi-statically (e.g. via RRC signalling) to the eNB using a bitmap.
[00122] Alternately, in another embodiment, a feedback method provides
independently selected sub-band feedback of Precoding Matrix Indicator (PMI),
Rank
Indicator (RI) and Channel Quality Indicator (CQI) for each TP. In a fading
environment, the channels from multiple TPs to the same UE may be completely
independent due to the geographical separation of the TPs. As a result,
applying
frequency selective scheduling for that UE on multiple TPs may require
assignment of
separate sub-bands to that UE for different TPs. This could result in a more
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frequency resource utilization across the cell(s) compared to a scenario where
UE is
assigned the same sub-band on all TPs.
[00123] Transmission on separate sub-bands of the same carrier from different
TPs
can be supported by feeding back separate PMIs/RIs/CQIs for each sub-band for
different TPs. However, the need to support sub-band CSI feedback for each TP
may
require a large amount of feedback. The amount of feedback can however be
significantly reduced by feeding back the CSI corresponding to selective parts
of the
bandwidth.
[00124] For example, the UE can only feedback the CSI of the best TP on each
sub-band. In this context, the best TP can be defined for example as the TP
offering
the highest throughput in that sub-band.
[00125] Also for example for each TP, the UE can feed back the CSI of only
those
sub-bands with good channel quality (with some certain criterion, for example,
overall SNR is above some thresholds). Alternatively the UE feeds back the CSI
on
the best M sub-bands for each TP. This is an extension of the UE-selected sub-
band
feedback which exists in the current specifications
[00126] These selective feedback approaches reduce the feedback, but may
impose
some limitations on the performance of the eNB scheduler. The feedback mode
(e.g.
feedback CSI on all sub-bands, or feedback CSI on selected sub-bands only)
could be
configured semi-statically through higher layer (e.g. RRC) signalling.
[00127] Accordingly, in certain embodiments, the UE feeds back single-cell
PMI/RI/CQI for each TP separately on some selected sub-bands. Depending on the
selection method and also the channel coefficients, the sub-bands on which the
UE
reports PMI/RI/CQI for different TPs may or may not overlap. A plurality of
sub-
band selection methods are contemplated. For example, for each sub-band, the
CSI of
the best TP or a number of best TPs is reported. The CSI and selected TP index
should be fed back for each sub-band. The criteria for determining the best TP
or TPs
may be defined based on throughput or received SNR. Also for example, for each
TP,
the CSI on a certain number of sub-bands is reported. These sub-bands could
include
those with good channel conditions or simply the best M sub-bands for that TP,
where
M is pre-defined and known by both transmitter and the receiver. For each TP,
the
CSI parameters and the indices of the best M selected sub-bands should be fed
back.
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[00128] In another embodiment, transmission schemes for enabling feedback
solutions that functions in conjunction with CoMP transmissions are set forth.
[00129] More specifically, in one embodiment the transmission schemes for
enabling feedback solutions provides forth.
[00130] When considering transmission schemes for enabling feedback solutions,
two main scenarios for CoMP operation can be considered. In the first
scenario, all
TPs in a CoMP set transmit DL data to a UE on the same frequency resources or
sub-
band at a given time. In the other scenario, TPs in the CoMP set may transmit
on
separate sub-bands to a UE on a given carrier at a given time. This is
motivated by the
fact that the channels from different TPs to the UE are statistically
independent and
separate frequency selective scheduling may be carried out for different TPs.
Since
TPs are geographically separated, this method may lead to more efficient
frequency
reuse and more flexibility in resource management across the cell. These two
scenarios are addressed in this section.
[00131] More specifically, in one embodiment, the transmission scheme for
enabling feedback solutions that function in conjunction with CoMP
transmissions
provides for a multi-point transmission on the same sub-bands with the same
codeword. With this transmission scheme, it is assumed that all TPs transmit
on the
same time/frequency resources.
[00132] Additionally with this transmission scheme, each TP i is assigned with
a
precoding matrix W, selected from existing codebooks. In general, the
dimensions of
Wis may be different, as the transmission rank and also the number of antenna
ports in
the TPs may be different. The transmission rank of TP i shall be denoted by
R1. By
assuming x is the vector (of length R = max R1) of data layers to be
transmitted
jointly by all TPs. For each TP, if its transmission rank R, is smaller than
the total
number of data layers R, another parameter is used to describe the assignment
of some
data layers in x to that specific TP. Thus, S, c {1, = = = ,R}, S1 = R is
defined as the
index set of data layers sent from TP i. The transmission can be described in
Equation (7) as
y = 1-1,Wix(S) + n (7)
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where x(Si) denotes the elements of x with indices in the set Si, it is the
channel
matrix from TP i to the UE, Wi is the precoder vector or matrix used by TP i,
and n is
the additive white Gaussian noise.
[00133] Accordingly, in certain embodiments, TPs transmit the same data layers
(or a subset of them) on the same frequency/time resources using different
precoding
matrices. If the rank of a precoder used by a TP is smaller than the number of
data
layers, a subset of the data layers is selected and transmitted by the
corresponding TP.
The subset of layers is known by the UE for CQI calculation purposes.
[00134] To support this scheme in the general case of unequal ranks, the
feedback
mechanism which feeds back PMI/RI/CQI for each TP plus common CQIs is used.
The selection method based on maximizing the throughput is described in
Equation 3.
The data layer assignments (parameters Si) may be predefined and known by both
the
UE and the TPs. Also, the data layer assignment may be dynamically derived,
for
example from Equation 3. In the latter case, some additional signalling is
likely
required to feedback Si. The eNB could make the final assignments based on the
feedback and other considerations and signal the assignment to the UE.
[00135] In a special case, where all TPs transmit with the same rank, the
feedback
mechanism which feeds back PMI/CQI for each TP plus a common RI/CQI can also
be used. In this case, the relation between the received signal and the data
layers is
simplified to:
(
y= x+n
[00136] In another embodiment, the transmission scheme for enabling feedback
solutions that function in conjunction with CoMP transmissions provides
distributed
beamforming with phase corrections.
[00137] This scheme is supported with the feedback mechanism which feeds back
PMI/RI/CQI for each TP plus common CQIs and phase differences, where some
additional feedback (in the form of phase differences between a TP and a
reference
TP) are available to the transmitter. As discussed with respect to this
feedback
mechanism, the additional feedback may partially compensate for the effects of
precoder codebook quantization and may yield larger beamforming gains. The
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scheme is described in Equation 5. The proposed scheme supports transmission
of
rank>1 by using one phase correction for each layer of data on each TP. This
is
different from certain known methods where only one phase value per UE is
used.
Also, this scheme allows for transmitting mixed ranks, i.e. different ranks
from
different TPs. This can be useful when the number of antenna ports varies
across the
TPs or when at a certain instance the fading channel of a TP is not sufficient
to
support as many data layers as other TPs do.
[00138] Accordingly, in certain embodiments, TPs transmit the same data layers
on
same time/frequency resources using different precoding matrices. Each data
layer k,
on TP i may be multiplied by eicsik , where sAk is a phase value fed back from
the UE.
Additionally, in certain embodiments, if the rank of a precoder is smaller
than the
number of data layers, a subset of data layers are transmitted by the
corresponding TP.
The subset is known by the UE for CQI calculation purposes.
[00139] In another embodiment, the transmission scheme for enabling feedback
solutions that function in conjunction with CoMP transmissions provides multi-
point
transmission on the same sub-bands with different codewords.
[00140] One way to utilize a multiple TP deployment structure is to use the
TPs for
increasing the transmission data rates delivered to the UE. As described with
respect
to the feedback mechanism which feeds back PMI/RICQI for each TP with rank-0
included, this can be realized by transmitting different data layers from
different TPs.
[00141] In known LTE specifications, the data layers are formed from one or
two
transport blocks (TB). Hence, all TPs transmit the same TB and therefore use
the
same CQI(s). However, it is possible to increase the number of TBs by
transmitting
different TBs from different TPs, and therefore supporting more than two TB
transmission to the UE. If that is the case, the use of TP-specific CQI
feedback may
be required. This scenario can be supported by the feedback mechanism which
feeds
back PMI/RICQI for each TP with rank-0 included.
[00142] Accordingly, in certain embodiments, TPs could transmit different data
layers on the same time/frequency resources. The data layers from different
TPs could
come from different transport blocks. More than two TBs could be transmitted
to the
same UE. Additionally, in certain embodiments, a TP may be assigned a rank-0
transmission. This should be signalled to the UE.
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[00143] In another embodiment, the transmission scheme for enabling feedback
solutions that function in conjunction with CoMP transmissions provides
transmit
diversity across TPs.
[00144] More specifically in certain embodiments where the transmission scheme
for enabling feedback solutions that function in conjunction with CoMP
transmissions
provides transmit diversity across TPs, an Alamouti code is applied across TPs
to
achieve diversity gain. As shown in Figure 10, the Alamouti codeword can be
applied
to a pair of REs, which can be either two consecutive (or otherwise closely-
spaced)
subcarriers in frequency (similar to SPBC coding) or can be two REs on the
same
subcarrier frequency but in two different (but preferably closely-spaced) time
instances (similar to STBC coding). Two layers of data are generated after
Alamouti
coding, each layer being dispatched to one TP, where precoding is applied
separately
before transmission. The precoding applied by each TP is based on the feedback
from
the UE for that particular TP. For a mathematical description of this method,
assume
Xi and x2 are two modulation symbols. On RE #1, TP1 transmits xi with a
precoder w1
and TP2 transmits x2 with a precoder w2. Hence, the UE receives
y1 = Hiwixi +112w2x2 +n1
[00145] At RE #2, assuming the channels do not change significantly over these
. .
two REs, TP1 transmits ¨ x2. with precoder wi and TP2 transmits xi with
precoder
w2. Hence, the UE receives
y2 = -111W1X2 +112W2X1 +n2
[00146] This is an Alamouti code with an effective channel matrix
Heff = [Hiwi H2w2]
[00147] To decode the Alamouti codes at the UE, separate DM-RS ports are used
for each TP. For example, DM-RS ports 7 and 8 as defined in Rel-10 could be
used
for each TP, which are transmitted on the same REs and separated by different
orthogonal codes. If such transmission is configured to the UE as a
transmission
mode, the DM-RS ports used could be pre-defined and may not need to be
signalled
to the UE.
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[00148] Accordingly, in certain embodiments, in a two TP CoMP set scenario,
each TP could transmit one layer of data on the same time/frequency resource
as the
other TP. Layer mapping to the TPs may be performed based on 2-tx transmit
diversity (Alamouti coding) as defined in LTE, but the Alamouti coded streams
could
then be precoded and transmitted by each TP separately. Separate DM-RS ports
would be used for each TP for data demodulation at UE.
[00149] Because the performance of the Alamouti code depends on the norm of
the
channel matrix, i.e.2 +1112W2121 , the optimum precoding vector w for TP i
can be chosen individually and solely based on the corresponding channel H1.
If the
number of TPs is more than two, TPs can be paired such that each pair
transmits one
Alamouti codeword but in a resource different from the resource used by other
pairs
(similar to 4-antenna Alamouti in LTE Re1-8 and Rel-10).
[00150] One approach is to transmit Alamouti codewords on orthogonal sub-
spaces. In other words, the precoding vectors should be chosen such that the
paired
layers from the two TPs occupy a single dimension in the received vector
space. Also,
different layers should be orthogonal at the receiver vector space. With this
method,
different data layers, corresponding to different Alamouti codewords, are
easily
decoupled at the receiver side and a simple Alamouti decoder can be applied.
[00151] An alternative approach for jointly selecting the precoding matrices
is to
derive the effective channel matrix in terms of actual channel matrices and
the
precoding matrices and choose the PMIs such that the capacity (corresponding
to the
effective channel matrix) is maximized. With this approach, a more advanced
receiver
structure may be needed for detecting the data.
[00152] In this method, all TPs should transmit with the same rank so that
layers
from two TPs can be paired to form an Alamouti codeword. Also, the data on
different TPs come from the same codeword. Hence, the TPs share the CQI as
well.
But, each TP may use a PMI different from other TPs. As a result, the feedback
mechanism which feeds back PMI/RICQI for each TP with rank-0 included may be
used to support this transmission mode.
[00153] In general, it is possible to transmit R layers of data from each TP
and to
apply an Alamouti code on each layer separately, an example of R=2 is shown in
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Figure 11 with two TPs. This leads to the transmission of multiple Alamouti
codewords on the same resources. The process of selecting the precoding
matrices is
more complicated in this general scenario and may be required to be performed
jointly for all TPs.
[00154] Accordingly, in certain embodiments, in a two TP CoMP set scenario,
TPs
may transmit the same number of data layers on the same time/frequency
resource.
Each layer of TP #1 is paired with one layer of TP #2 and layer mapping is
performed
such that each pair of layers forms an Alamouti code. A separate DM-RS port
could
be used for each layer transmitted from each of the TPs.
[00155] In another embodiment, the transmission scheme for enabling feedback
solutions that function in conjunction with CoMP transmissions provides inter-
TP
transmit diversity without precoding.
[00156] An inter-TP transmit diversity scheme with precoding is described
above
which exploits both precoding and transmit diversity gains. In an alternate
embodiment, if each of two TPs has one antenna port, the precoding operation
can be
skipped, and each pair of symbols after Alamouti coding could be dispatched to
each
TP and transmitted without precoding.
[00157] If each of the two TPs has two antenna ports, the 4-tx transmit
diversity
scheme as adopted in LTE Re1-8, or so-called SFBC+FSTD, can be applied across
the
total of four antenna ports from two TPs. This scheme would only benefit from
the
diversity gain, but it has the advantage that it does not require PMI feedback
from the
UE, and therefore, could improve the performance of UEs having relatively high
mobility.
[00158] To decode Alamouti codes, TP specific RS are transmitted from each TP.
As common RS (CRS) may need to be transmitted from all TPs to support legacy
UE,
DM-RS ports as defined in Re1-9/10 could be reused for this purpose or new TP
specific RS ports could be defined. No precoding is applied to DM-RS ports
within
the assigned RBs.
[00159] Accordingly, in certain embodiments, Re1-8 2-tx and 4-tx transmit
diversity are applied across TPs to form transmit diversity for CoMP
transmission.
TP specific RS ports may be defined or DM-RS ports as defined in Re1-9/10 may
be
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reused for channel estimation where no precoding is applied to DM-RS ports
within
as signed RBs.
[00160] In another embodiment, the transmission scheme for enabling feedback
solutions that function in conjunction with CoMP transmissions provides open-
loop
spatial multiplexing CoMP transmission.
[00161] In this transmission, the same layers of data could be transmitted
from
different TPs or different layers of data could be transmitted from different
TPs, and
either no precoding or a pre-defined precoding are applied at the TPs. No PMI
feedback is needed, only CQI is fed-back from the UE.
[00162] In another embodiment, the transmission scheme for enabling feedback
solutions that function in conjunction with CoMP transmissions provides multi-
point
transmission on separate sub-bands.
[00163] In a CoMP scenario, where TPs are geographically separated, their
large-
scale fading (shadowing) and small-scale fading (multipath) channels to the UE
are
both independent from each other. Hence, if a UE sees a good channel from one
TP
on a sub-band, it does not necessarily lead to the UE seeing good channels
from other
TPs on the same sub-band. In such a situation, forcing all TPs to use the same
sub-
band for transmission to the same UE may prevent the system from fully
exploiting
the potential gain that is available through frequency selective scheduling.
In other
words, by allowing the TPs to transmit on separate sub-bands, they can
individually
carry out frequency selective scheduling which could lead to performance gains
for
each UE. From the system level point of view, compared to transmission on the
same
sub-bands from all TPs, this approach may require an overall larger bandwidth
for
transmission to the UE. However, it should be noted that by having frequency
reuse
across the cell(s), the overall bandwidth utilization may not be affected by
this
approach. For example, in Figure 12, UE 1 is scheduled on sub-band 1 (sb 1)
from TP
#1 and sub-band 2 (sb 2) from TP #2, because the corresponding channels on
those
sub-bands are the best for each respective TP. At the same time, TP #3 can
reuse sb 1
to service UE #2. Since UE#2 is in the coverage area of TP #2, sb 2 could not
be used
for it as TP #2 already used sb 2 to serve UE #1. It should be noted that
separate sub-
band transmission provides the scheduler with more flexibility which could
allow for
more efficient scheduling.
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[00164] Accordingly, in certain embodiments, transmission on separate sub-
bands
from different TPs could be used to fully exploit the frequency selective
scheduling
gains available from multiple TP to UE propagation channels. If the same MCS
and
same TB is used for all sub-bands, transmission on separate (non-overlapping)
sub-
bands from multiple TPs may be supported by reusing the current downlink grant
structure (DCI) as defined in Re1-8. Otherwise, the DL grant structure may
need to be
changed to accommodate the overhead required for supporting transmission on
separate sub-bands (for example, instructing the UE which RBs it is scheduled
on and
which MCSs are used).
[00165] More specifically, in certain embodiments, the transmission scheme for
enabling feedback solutions that function in conjunction with CoMP
transmissions
provides multi-point transmission on separate sub-bands use codeword
splitting.
[00166] If a UE is scheduled to receive data from multiple TPs on different
sub-
bands, one possibility is to split each codeword into different segments and
transmit
each segment via a different TP. An example of codeword splitting is shown in
Figure
13. CRC attachment, code block segmentation, channel coding, rate matching,
and
code block concatenation are performed as defined in the known specifications
(see
e.g., 3GPP TSG-RAN TS 36.212). Rate matching is performed based on the total
number of REs assigned to all TPs. The codeword length at the output of code
block
concatenation is denoted by G. By codeword splitting the whole codeword is
broken
into n disjoint segments, where segment i has length Gi and is sent to TP #i
for further
processing, i.e. scrambling, modulation, layer mapping, precoding, etc. The
segment
lengths Gi are arranged such that G = G..
[00167] The splitting shown in Figure 13 is an example in which the first G1
coded
bits are assigned to TP #1, the next G2 bits are assigned to TP #2, and so on.
In
general, any segmentation of the codeword would work. Codeword splitting
mentioned here is different from code block segmentation which is part of the
channel
coding.
[00168] The codeword splitting in Figure 13 is shown for a single codeword
only.
If the UE is scheduled for more than one codeword, the same procedure can be
applied for each codeword separately.
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[00169] If different TPs have the same cell ID, as in CoMP scenario 4 with
RRHs,
the scrambling sequences for all TPs may be the same. In such a scenario, most
of the
processing can be performed in a central unit, say at a Macro eNB, and the
precoded
signals can be sent to the TPs for resource mapping and transmission. This is
suitable
for scenarios when the RRHs have low processing capabilities.
[00170] To support this scheme, the feedback from a UE can include separate
PMIs, RIs, and CQIs for all the associated TPs on all the sub-bands. This can
be
performed by the feedback mechanism which feeds back PMI/RICQI for each TP
with rank-0. However, in this scenario, there is no need for joint calculation
of the
CSI and the CSI of each TP is calculated as in a single-cell manner (because
on each
sub-band only one TP transmits to the UE). To reduce feedback overhead, the UE
can use a selective feedback mechanism which independently selects sub-band
feedback of PMIs/RIs/CQIs for each TP. Examples of this include feeding back
the
CSI of the best TP for each sub-band or, feeding back the best M sub-bands for
each
TP.
[00171] To support this scheme, the eNB may need to derive a common CQI for
MCS assignment. One way to derive this information is to use the wideband CQI
feedback from the UE. Alternatively, eNB can use the CQIs which are available
to it
for all scheduled sub-bands to derive a single CQI for obtaining the MCS. One
approach for doing this is to use the worst CQI amongst all CQIs of allocated
sub-
bands. An alternative approach is to estimate the SNR of each sub-band based
on its
CQI and then average over them (for example by using the Exponential Effective
SNR Mapping ¨ EESM). The averaged SNR can be used to obtain a single CQI for
all
sub-bands and from which the MCS to be used over these separate sub-bands is
determined. If a single CQI is derived at the eNB, only one MCS should be
included
in the DL grant. Hence, the existing LTE downlink grant structure defined in
Rel-
8/9/10 could be reused. By doing this, transmission on separate sub-bands from
different TPs could be transparent to the UE as the UE does not need to know
which
sub-band is transmitted from which TP.
[00172] Accordingly, in certain embodiments, different TPs may transmit
different
portions of a codeword on separate sub-bands. A single MCS is used across all
the
sub-bands scheduled.
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[00173] In certain embodiments, the transmission scheme for enabling feedback
solutions that function in conjunction with CoMP transmissions provides multi-
point
transmission by transmitting the same codeword (TB) on different sub-bands.
[00174] More specifically, in this alternative approach for taking advantage
of
transmission on separate sub-bands, the output of the channel encoder is used
by all
TPs. However, each TP applies a rate matching processing operation separate
from
other TPs. As shown in Figure 14, the output of the channel coding is sent to
all TPs,
and each TP, depending on its number of REs, applies rate matching and then
code
block concatenation.
[00175] In this scheme, different TPs can use different MCSs and there is no
need
for averaging the CQIs.
[00176] Since the same data is transmitted on multiple uncorrelated sub-bands,
frequency diversity gain is expected if the receiver is designed properly.
This may be
performed by calculating the log-likelihood ratios (LLRs) of information bits
on each
sub-band and then combining them together before making a hard decision.
[00177] Any feedback mechanism that provides single cell PMIs, RIs, and CQIs
can be used. To support this scheme, a downlink grant is designed to allocate
different MCS for each sub-band, while maintaining one TB for the whole data
traffic.
[00178] More specifically, in certain embodiments, different TPs may use the
output of the same channel encoder and apply rate matching separately. Then,
each
TP may transmit its codeword on a separate sub-band from other TPs. Different
MCS
are assigned to each sub-band and this information needs to be signalled to
the UE.
[00179] In certain embodiments, the transmission scheme for enabling feedback
solutions that function in conjunction with CoMP transmissions provides multi-
point
transmission by transmitting separate codeword(s) on separate sub-bands.
[00180] CoMP structures can be used to increase the data rate or the
multiplexing
gain of the UEs. Separate sub-band transmission from different TPs is a
scenario
which readily allows exploitation of this potential of CoMP. When different
TPs are
scheduled to transmit on separate sub-bands to serve a UE, each TP can
transmit a
separate codeword or TB. As each TP could transmit on different sub-band, the
MCSs
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corresponding to these codewords may be also different. This way, multiple TBs
can
be transmitted to the UE at the same time on different sub-band.
[00181] The feedback mechanism which provides single cell separate CSI
feedback or single cell selective feedback may be used with this transmission
scheme.
[00182] To support this scheme, separate downlink grants may be used to
schedule
different data transmission to the UE. In another embodiment, a new downlink
grant
may be designed which includes different MCS assignment for separate sets of
sub-
bands transmitted from different TPs.
[00183] Accordingly, in certain embodiments, each TP may have a separate TB on
which the TP applies channel coding. Different MCS may be assigned to each TB.
The different TBs can then be transmitted on separate sub-bands from different
TPs.
[00184] In other embodiments, methods for configuring feedback and
transmission
schemes that functions in conjunction with CoMP transmissions are set forth.
[00185] The various feedback schemes and transmission schemes described may
be applied to different scenarios. However, to reduce the complexity at both
eNB and
UE to support CoMP transmission, it is preferable to allow these schemes to be
configurable. On the other hand, it is desirable to allow enough flexibility
at the eNB
to determine which transmission schemes may be used for each sub-frame, and
such
switching between transmission and feedback schemes should preferably bring
about
minimum or no impact to the UE.
[00186] More specifically, in one embodiment, a method for configuring
feedback
schemes that functions in conjunction with CoMP transmissions is set forth.
[00187] As discussed, there are various ways for the UE to derive the
appropriate
PMI, RI and CQI and feed them back to the eNB. Such methods of deriving these
parameters could be a UE implementation issue as long as they meet certain
performance requirements. In general, for multiple TPs, different PMI needs to
be
derived and fed back. For RI and CQI, there are different approaches, either
deriving
and feeding back separate RI and CQI for each TP, or deriving and feeding back
common RI and CQI for all the TPs.
[00188] Another consideration in feedback design is that of backwards
compatibility. Generally, it is preferable to reuse existing feedback schemes
(modes)
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where possible (i.e., modes developed in previous specification releases) and
thus
reduce the impacts arising from the introduction of new schemes on the UE
complexity. Certainly some modifications on these existing modes may need to
be
considered.
[00189] Some principles which may be used as the baseline for feedback design
in
closed-loop CoMP transmission are shown in Figure 15. More specifically,
Figure 15
shows a feedback reporting example using time division multiplexing, in which
it is
assumed that a joint rank (across TPs) is derived and fed back via uplink
channels to
the eNB (e.g., via PUCCH or PUSCH). Subsequent to such a rank report, a
CQI/PMI
report could be fed back to TP #1, followed by a CQI/PMI report to TP#2. The
same
reporting formats as defined in Re1-8 could be used for these two reports and
they
may be transmitted via PUCCH or PUSCH in subsequent subframes. Following this,
a joint CQI report could also be fed back.
[00190] Alternatively, the rank report, individual PMI/CQI reports for each TP
and
joint CQI report for a plurality of TPs could be encoded and transmitted
together.
Transmission of such a jointly-encoded multi-TP feedback report would be more
suited to transmission on PUSCH although modification of PUCCH to accommodate
these is also possible.
[00191] Accordingly, a plurality of embodiments relate to feedback reporting
for
closed-loop CoMP transmission. For example, one embodiment relates to
supporting
feedback of common rank (one rank for all TPs) or separate ranks for each TP.
Separate ranks for each TP could be jointly coded and fed-back together within
the
same rank report. In another embodiment, for each TP, separate CQI/PMI reports
as
defined in Re1-8 or Rel-10 could be fed back to the eNB. The CQI feedback in
such
reports could assume single TP transmission and could be derived in the same
way as
defined in previous releases. In another embodiment, the CQI/PMI reports for
each
TP could be transmitted in either PUCCH or PUSCH. Different reports for
different
TPs could be transmitted in different subframes (e.g., transmitted in periodic
report on
PUCCH) in a time multiplexed (TDM) manner. If subband CQI/PMI reports for each
TP is configured, such reports could be transmitted on PUCCH in a time
multiplexed
(TDM) manner that subband CQI/PMI reports for one TP is transmitted in
sequence
followed by those for second TP and so on. Or subband CQI/PMI reports of
different
TPs are interleaved in a sequence and transmitted in different PUCCHs.
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Alternatively, all reports for different TPs could be multiplexed and/or
encoded
together (e.g. sent within an aperiodic report on PUSCH). In another
embodiment, in
addition to the above reports, CQI reports could be configured in which a
joint CQI is
derived assuming that the same layers of data would be transmitted from each
TP.
Such reports could be transmitted in a multiplexed fashion with other CQI/PMI
reports in TDM manner (e.g. on PUCCH using a periodic reporting structure) or
multiplexed with other CQI/PMI reports and encoded and/or transmitted together
(e.g.
on PUSCH as an aperiodic report). In another alternative, CSI feedback
reporting
could be transmitted on both PUCCH and PUSCH, for example, RI report, wideband
CQI/PMI report per TP and wideband joint CQI could be transmitted on PUCCH in
a
TDM manner, while subband PMI/CQI for each TP and subband joint CQI could be
transmitted on PUSCH.
[00192] In known specification releases, different types of feedback modes are
defined which derive and report different types of CQI/PMI including wideband
reporting, selected sub-band reporting and all sub-band reporting. With the
introduction of multiple TPs in the system which support CoMP operation, the
feedback reports for different TPs could follow the same reporting style as
previously
defined.
[00193] Additionally, a plurality of other embodiments relate to closed-loop
CoMP
transmission. For example, in one embodiment, the Re1-8 feedback modes 1-1, 2-
1
for PUCCH, and modes 3-1, 1-2 and 2-2 for PUSCH could be extended for closed-
loop transmission. In such modes, for each TP, the same types of feedback
reports as
defined in Re1-8 could be used. In addition, joint CQI reports could be
derived and
fed-back. In another embodiment, for selected sub-band reporting, the
selection of
best-M sub-bands can be based on joint CQI from multiple TPs instead of
individual
CQI for each TP. The UE could then derive and feedback separate CQI/PMI
reporting for each TP based on selected sub-bands but assuming individual
transmission from each TP. The UE could in addition derive and feedback joint
CQIs
for each selected sub-band by assuming joint transmission from all TP.
[00194] For CoMP transmit diversity and open-loop spatial multiplexing
transmission, CQI only feedback could be considered. The feedback modes could
be
based on modes 1-0 and 2-0 on PUCCH, or modes 2-0 and 3-0 on PUSCH, and
separate CQIs for each TP are reported. Joint RI/CQI reports could be fed back
for
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open-loop CoMP transmission on top of separate CQI feedback for each TP, which
would allow the eNB to dynamically switch between CoMP and individual per TP
transmission.
[00195] A plurality of embodiments relate to open-loop CoMP transmission. For
example, the feedback modes 1-0, 2-0 for PUCCH, and modes 2-0, 3-0 for PUSCH
could be considered as the baseline for feeding back separate CQI for each TP.
Also
for example, joint CQI derived based on transmission from all TP could be
included
in the feedback
[00196] The feedback modes could be semi-statically configured through higher-
layer (e.g. RRC) signalling similar to feedback configurations in previous
release.
[00197] In another embodiment, a method for configuring transmission schemes
that function in conjunction with CoMP transmissions is set forth.
[00198] With the feedback modes as described, the eNB can configure the UE to
feedback separate CQI/PMI reporting for each TP. In addition the eNB can
configure
UE to derive and feedback joint CQI feedback reporting for all TPs, This
allows
enough flexibility at the eNB for its scheduling. For example, the eNB can
schedule
joint transmission or simply schedule single TP transmission to the UE. By
doing so,
a single closed-loop CoMP transmission mode can be configured which
accommodates dynamic switching between CoMP and non-CoMP transmission.
[00199] In CoMP transmission, a plurality of transmissions can be supported as
long as there exists a 1-to-1 mapping between DM-RS ports and layers. These
transmissions would be the same to the UE in terms of UE reception. For
example, a
transmission where two TPs each transmit a different layer to the UE is
supported.
Also for example, a transmission where two TPs each transmit the same two
layers to
the UE is supported.
[00200] Other transmission modes could be configured for CoMP transmission.
For example, the transmit diversity with precoding scheme could be configured.
Alternatively, the transmit diversity without precoding could also be
configured.
[00201] Accordingly, in certain embodiments, the network is able to configure
the
use of a closed-loop spatial multiplexing CoMP transmission modes. The
transmission mode could support separate CQI/PMI reporting for each TP. In
addition, a joint CQI feedback could be configured. Dynamic switching between
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CoMP and non-CoMP transmission could be supported by this mode. Also, in
certain
embodiments, the network is able to configure the use of an open-loop spatial
multiplexing CoMP transmission mode, which does not need PMI feedback from the
UE. Pre-defined or eNB determined precoding vectors could be applied at the
TPs.
Also, in certain embodiments, closed-loop and open-loop spatial multiplexing
CoMP
transmissions could be included within one transmission mode termed Spatial
multiplexing CoMP transmission mode. The configuration of different feedback
modes in the UE are used to achieve switching between closed-loop and open-
loop
operation. For example, if the UE is configured with CQI only (no PMI)
feedback,
open-loop transmission would be used, whilst if the UE is configured with
PMI/CQI
feedback, closed-loop transmission would be used. Also, in certain
embodiments,
transmit diversity with or without precoding could be configured for two TPs.
Alamouti types of encoding could be applied to generate pairs of coded
symbols,
these pairs being potentially transmitted from different TPs. CQI calculation
at the UE
for feedback needs to assume Alamouti coding is used. Transmit diversity
across
multiple TPs could be configured as a separate transmission mode or could be
used as
a fall-back scheme for joint spatial multiplexing transmission across multiple
TPs.
[00202] In another embodiment, a method for configuring transmission schemes
which provides DCI support for CoMP transmission is set forth.
[00203] Known DCI formats could be reused for CoMP transmission, thus making
the CoMP transmission transparent to the UE, or at least minimising its impact
on
existing signalling structures. In joint transmission, (wherein the same data
layers are
transmitted from multiple TPs), the same DM-RS ports could be used for each
TP.
Therefore, there is no need to signal additional DM-RS ports and a single DCI
format
such as DCI format 2C for TM9 could be used. If different layers are
transmitted from
different TPs, different DM-RS ports would need to be assigned to each TP.
However,
as long as there is a 1-to-1 association between a DM-RS port and a layer, no
additional signalling is needed for UE demodulation. In general, up to four DM-
RS
ports need to be supported for CoMP transmission.
[00204] In other embodiments, methods for allowing a CSI-RS transmission in a
cell with a plurality of TPs sharing the same cell ID are set forth.
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[00205] One motivation behind the proposed scheme is to share the same CSI-RS
configuration between different TPs in a frequency division manner. It is
envisioned
that by doing so, fewer CSI-RS configurations are needed in a cell and UE
complexity
in deriving CSI from these CSI-RS is reduced.
[00206] In one embodiment, one Rel-10 CSI-RS configuration is used for the
macro eNB. The same configuration is also used by the RRHs. This configuration
is
signalled to all Rel-10 and post Rel-10 UEs. Another CSI-RS configuration is
used for
RRHs and is signalled to newer UEs only (e.g. those supporting CoMP). These
two
CSI-RS configurations may differ only by the CSI-RS patterns in a subframe.
The
second CSI-RS configuration is shared between all RRHs in a frequency division
multiplexing fashion. Because the CSI-RS configuration is applicable to all
RBs in
the system bandwidth, each RRH transmits CSI-RS on a specific sub-band
(frequency
band) in each configured CSI-RS subframe. The sub-band containing CRS-RS for
each RRH may hop from one CSI-RS subframe to another so that the full system
bandwidth may be covered after certain number of CSI-RS subframes. The number
of subframes needed to cover the whole bandwidth by a single RRH is equal to
the
number of RRHs in a cell. The hopping scheme could be either a specific
pattern or as
illustrated in Figure 16, where the sub-band position of each RRH is shifted
cyclically
at each transmission opportunity.
[00207] For example, suppose a macro eNB with 2 RRHs in a 10MHz system
bandwidth. The CSI-RS configuration as shown in Figure 17 uses resource
element
(RE) #9 of ODFM symbol #5 and #6 for antenna port 0/1, and resource element
(RE)
#2 of OFDM symbol #5 and #6 in each RB for antenna port 2/3. The scheme shares
the CSI-RS configuration pattern between 2 RRHs as follows: the configuration
is
allocated for RRH1 for the frequency region spanning from RB#0 to 24 and then
the
same configuration is allocated for RRH2 for the frequency region
corresponding to
RB #25 to49 where in this example the total number of RB in a 10 MHz system
bandwidth is 50. The number of sub-bands (corresponding to the number of RRHs)
and the number of antenna ports per sub-band need to be signalled as extra
information in a semi-static (e.g. RRC) message to a set of UEs supporting
CoMP
(e.g. Rd-11 UEs). The size in RBs of the different sub-bands may also be
signalled if
they are different. This allocation will then cycle in time, so that the UE is
able to
measure the wideband channel from each RRH as depicted Figure 16. The cycling
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period and pattern can be varying and depend on the number of RRHs and channel
conditions.
[00208] The number of antenna ports per RRH needs to be signalled only once in
a
semi-static manner. Knowing the number of sub-bands and the RRH hopping
pattern,
the UE can derive the number of antenna ports supported in each sub-band in
each
CSI-RS subframe as the RRHs hop over the sub-bands in time.
[00209] The scheme presented above could be extended in a plurality of
different
ways. For example, to increase the accuracy of the CSI measurements, the whole
macro eNB coverage area could be divided into regions, where each region is
configured with one CSI-RS configuration for UEs supporting CoMP, and each
region contains more than one RRH. All the RRHs in the same region would share
the
same CSI-RS configuration as described above. This would allow CoMP UEs to
report CSI only for the configured RRHs instead of reporting CSI for all RRHs.
[00210] Another extension includes the RRH sharing the same configuration
(same
resources/pattern, offset, periodicity) across the whole band, but the CSI-RS
for each
RRH are differentiated by CDM (code division multiplexing).
[00211] Such a scheme for allowing a CSI-RS transmission in a cell with a
plurality of TPs sharing the same cell ID provides a plurality of advantages.
For
example, such methods are backward compatible for legacy UEs. The scheme
presented above is transparent to non-CoMP (e.g. Rel-10) UEs. A configuration
is
reserved for the macro-eNB and is signalled to Rel-10 UEs and post Rel-10 UEs.
Additionally, with such a scheme, the need of RRH association for CSI feedback
is
removed. The eNB uses the feedback now to semi-statically reconfigure CSI-RS
configuration if needed since it has a total feedback from all RRHs.
Additionally,
such a scheme reduces unnecessary signalling overhead. The eNB needs not track
when the UEs are moving between RRHs hence will not need to signal a new CSI-
configuration each time. Additionally, with such a scheme, the CSI latency
feedback
report is reduced since only one offset is used. The periodicity can be
adapted to the
number of RRH supported in the macro eNB cell or the region. Additionally,
such a
scheme reduces impact of interference on adjacent cells since only one extra
CSI-RS
configuration is needed. Additionally, with such a scheme, rate matching is
simplified since the location of the CSI-RS are known and fixed. Additionally,
with
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such a scheme there is no need for signalling every time a UE moves from one
RRH
coverage to another. The artificial handover kind of problem created by the
existing
scenario is removed. Additionally, the management and assignment of CSI-RS
configuration is simplified.
[00212] Accordingly, in certain embodiments, CSI-RS for each TP has the same
pattern and transmits on the same bandwidth, but from different sub-bands. The
sub-
band on which the CSI-RS are transmitted for each TP hops across the whole
system
bandwidth over time. The hopping pattern of CRS-RS for each TP follows the
same
cycle but with different offset. The CSI-RS for macro-eNB can be transmitted
following the same rule as a TP or can be transmitted separately across the
whole
system bandwidth.
[00213] Figure 18 illustrates an example of a system 1800 suitable for
implementing one or more embodiments disclosed herein. In various embodiments,
the system 1800 comprises a processor 1810, which may be referred to as a
central
processor unit (CPU) or digital signal processor (DSP), network connectivity
interfaces 1820, random access memory (RAM) 1830, read only memory (ROM)
1840, secondary storage 1850, and input/output (I/0) devices 1860. In some
embodiments, some of these components may not be present or may be combined in
various combinations with one another or with other components not shown.
These
components may be located in a single physical entity or in more than one
physical
entity. Any actions described herein as being taken by the processor 1810
might be
taken by the processor 1810 alone or by the processor 1810 in conjunction with
one or
more components shown or not shown in Figure 18.
[00214] The processor 1810 executes instructions, codes, computer programs, or
scripts that it might access from the network connectivity interfaces 1820,
RAM 1830,
or ROM 1840. While only one processor 1810 is shown, multiple processors may
be
present. Thus, while instructions may be discussed as being executed by a
processor
1810, the instructions may be executed simultaneously, serially, or otherwise
by one
or multiple processors 1810 implemented as one or more CPU chips.
[00215] In various embodiments, the network connectivity interfaces 1820 may
take the form of modems, modem banks, Ethernet devices, universal serial bus
(USB)
interface devices, serial interfaces, token ring devices, fiber distributed
data interface
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(FDDI) devices, wireless local area network (WLAN) devices, radio transceiver
devices such as code division multiple access (CDMA) devices, global system
for
mobile communications (GSM) radio transceiver devices, long term evolution
(LTE)
radio transceiver devices, worldwide interoperability for microwave access
(WiMAX)
devices, and/or other well-known interfaces for connecting to networks,
including
Personal Area Networks (PANs) such as Bluetooth. These network connectivity
interfaces 1820 may enable the processor 1810 to communicate with the Internet
or
one or more telecommunications networks or other networks from which the
processor 1810 might receive information or to which the processor 1810 might
output information.
[00216] The network connectivity interfaces 1820 may also be capable of
transmitting or receiving data wirelessly in the form of electromagnetic
waves, such
as radio frequency signals or microwave frequency signals. Information
transmitted
or received by the network connectivity interfaces 1820 may include data that
has
been processed by the processor 1810 or instructions that are to be executed
by
processor 1810. The data may be ordered according to different sequences as
may be
desirable for either processing or generating the data or transmitting or
receiving the
data.
[00217] In various embodiments, the RAM 1830 may be used to store volatile
data
and instructions that are executed by the processor 1810. The ROM 1840 shown
in
Figure 18 may likewise be used to store instructions and data that is read
during
execution of the instructions. The secondary storage 1850 is typically
comprised of
one or more disk drives or tape drives and may be used for non-volatile
storage of
data or as an overflow data storage device if RAM 1830 is not large enough to
hold
all working data. Secondary storage 1850 may likewise be used to store
programs
that are loaded into RAM 1830 when such programs are selected for execution.
The
I/0 devices 1860 may include liquid crystal displays (LCDs), Light Emitting
Diode
(LED) displays, Organic Light Emitting Diode (OLED) displays, projectors,
televisions, touch screen displays, keyboards, keypads, switches, dials, mice,
track
balls, voice recognizers, card readers, paper tape readers, printers, video
monitors, or
other well-known input/output devices.
[00218] Figure 19 shows a wireless-enabled communications environment
including an embodiment of a client node as implemented in an embodiment of
the
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invention. Though illustrated as a mobile phone, the client node 1902 may take
various forms including a wireless handset, a pager, a smart phone, or a
personal
digital assistant (PDA). In various embodiments, the client node 1902 may also
comprise a portable computer, a tablet computer, a laptop computer, or any
computing device operable to perform data communication operations. Many
suitable
devices combine some or all of these functions. In some embodiments, the
client
node 1902 is not a general purpose computing device like a portable, laptop,
or tablet
computer, but rather is a special-purpose communications device such as a
telecommunications device installed in a vehicle. The client node 1902 may
likewise
be a device, include a device, or be included in a device that has similar
capabilities
but that is not transportable, such as a desktop computer, a set-top box, or a
network
node. In these and other embodiments, the client node 1902 may support
specialized
activities such as gaming, inventory control, job control, task management
functions,
and so forth.
[00219] In various embodiments, the client node 1902 includes a display 1904.
In
these and other embodiments, the client node 1902 may likewise include a touch-
sensitive surface, a keyboard or other input keys 1906 generally used for
input by a
user. The input keys 1906 may likewise be a full or reduced alphanumeric
keyboard
such as QWERTY, Dvorak, AZERTY, and sequential keyboard types, or a
traditional
numeric keypad with alphabet letters associated with a telephone keypad. The
input
keys 1906 may likewise include a trackwheel, an exit or escape key, a
trackball, and
other navigational or functional keys, which may be inwardly depressed to
provide
further input function. The client node 1902 may likewise present options for
the user
to select, controls for the user to actuate, and cursors or other indicators
for the user to
direct.
[00220] The client node 1902 may further accept data entry from the user,
including numbers to dial or various parameter values for configuring the
operation of
the client node 1902. The client node 1902 may further execute one or more
software
or firmware applications in response to user commands. These applications may
configure the client node 1902 to perform various customized functions in
response to
user interaction. Additionally, the client node 1902 may be programmed or
configured over-the-air (OTA), for example from a wireless network access node
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1908 (e.g., a base station), a server node 1916 (e.g., a host computer), or a
peer client
node 1902.
[00221] Among the various applications executable by the client node 1902 are
a
web browser, which enables the display 1904 to display a web page. The web
page
may be obtained from a server node 1916 through a wireless connection with a
wireless network 1912. As used herein, a wireless network 1912 broadly refers
to any
network using at least one wireless connection between two of its nodes. The
various
applications may likewise be obtained from a peer client node 1902 or other
system
over a connection to the wireless network 1912 or any other wirelessly-enabled
communication network or system.
[00222] In various embodiments, the wireless network 1912 comprises a
plurality
of wireless sub-networks (e.g., cells with corresponding coverage areas). As
used
herein, the wireless sub-networks may variously comprise a mobile wireless
access
network or a fixed wireless access network. In these and other embodiments,
the
client node 1902 transmits and receives communication signals, which are
respectively communicated to and from the wireless network nodes by wireless
network antennas (e.g., cell towers). In turn, the communication signals are
used by
the wireless network access nodes to establish a wireless communication
session with
the client node 1902. As used herein, the network access nodes broadly refer
to any
access node of a wireless network. The wireless network access nodes may be
respectively coupled to wireless sub-networks, which may in turn be connected
to the
wireless network 1912.
[00223] In various embodiments, the wireless network 1912 is coupled to a
physical network 1914, such as the Internet. Via the wireless network 1912 and
the
physical network 1914, the client node 1902 has access to information on
various
hosts, such as the server node 1916. In these and other embodiments, the
server node
1916 may provide content that may be shown on the display 1904 or used by the
client node processor 1810 for its operations. Alternatively, the client node
1902 may
access the wireless network 1912 through a peer client node 1902 acting as an
intermediary, in a relay type or hop type of connection. As another
alternative, the
client node 1902 may be tethered and obtain its data from a linked device that
is
connected to the wireless network 1912. Skilled practitioners of the art will
recognize
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that many such embodiments are possible and the foregoing is not intended to
limit
the spirit, scope, or intention of the disclosure.
[00224] Figure 20 depicts a block diagram of an exemplary client node as
implemented with a digital signal processor (DSP) in accordance with an
embodiment
of the invention. While various components of a client node 1902 are depicted,
various embodiments of the client node 1902 may include a subset of the listed
components or additional components not listed. As shown in Figure 20, the
client
node 1902 includes a DSP 2002 and a memory 2004. As shown, the client node
1902
may further include an antenna and front end unit 2006, a radio frequency (RF)
transceiver 2008, an analog baseband processing unit 2010, a microphone 2012,
an
earpiece speaker 2014, a headset port 2016, a bus 2018, such as a system bus
or an
input/output (I/0) interface bus, a removable memory card 2020, a universal
serial
bus (USB) port 2022, a short range wireless communication sub-system 2024, an
alert
2026, a keypad 2028, a liquid crystal display (LCD) 2030, which may include a
touch
sensitive surface, an LCD controller 2032, a charge-coupled device (CCD)
camera
2034, a camera controller 2036, and a global positioning system (GPS) sensor
2038,
and a power management module operably coupled to a power storage unit, such
as a
battery. In various embodiments, the client node 1902 may include another kind
of
display that does not provide a touch sensitive screen. In one embodiment, the
DSP
2002 communicates directly with the memory 2004 without passing through the
input/output interface 2018.
[00225] In various embodiments, the DSP 2002 or some other form of controller
or
central processing unit (CPU) operates to control the various components of
the client
node 1902 in accordance with embedded software or firmware stored in memory
2004
or stored in memory contained within the DSP 2002 itself. In addition to the
embedded software or firmware, the DSP 2002 may execute other applications
stored
in the memory 2004 or made available via information carrier media such as
portable
data storage media like the removable memory card 2020 or via wired or
wireless
network communications. The application software may comprise a compiled set
of
machine-readable instructions that configure the DSP 2002 to provide the
desired
functionality, or the application software may be high-level software
instructions to be
processed by an interpreter or compiler to indirectly configure the DSP 2002.
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[00226] The antenna and front end unit 2006 may be provided to convert between
wireless signals and electrical signals, enabling the client node 1902 to send
and
receive information from a cellular network or some other available wireless
communications network or from a peer client node 1902. In an embodiment, the
antenna and front end unit 1806 may include multiple antennas to support beam
forming and/or multiple input multiple output (MIMO) operations. As is known
to
those skilled in the art, MIMO operations may provide spatial diversity which
can be
used to overcome difficult channel conditions or to increase channel
throughput.
Likewise, the antenna and front end unit 2006 may include antenna tuning or
impedance matching components, RF power amplifiers, or low noise amplifiers.
[00227] In various embodiments, the RF transceiver 2008 provides frequency
shifting, converting received RF signals to baseband and converting baseband
transmit signals to RF. In some descriptions a radio transceiver or RF
transceiver
may be understood to include other signal processing functionality such as
modulatioWdemodulation, coding/decoding, interleaving/deinterleaving,
spreading/despreading, inverse fast Fourier transforming (IFFT)/fast Fourier
transforming (FFT), cyclic prefix appending/removal, and other signal
processing
functions. For the purposes of clarity, the description here separates the
description of
this signal processing from the RF and/or radio stage and conceptually
allocates that
signal processing to the analog baseband processing unit 2010 or the DSP 2002
or
other central processing unit. In some embodiments, the RF Transceiver 2008,
portions of the Antenna and Front End 2006, and the analog base band
processing unit
2010 may be combined in one or more processing units and/or application
specific
integrated circuits (ASICs).
[00228] The analog baseband processing unit 2010 may provide various analog
processing of inputs and outputs, for example analog processing of inputs from
the
microphone 2012 and the headset 2016 and outputs to the earpiece 2014 and the
headset 2016. To that end, the analog baseband processing unit 2010 may have
ports
for connecting to the built-in microphone 2012 and the earpiece speaker 2014
that
enable the client node 1902 to be used as a cell phone. The analog baseband
processing unit 2010 may further include a port for connecting to a headset or
other
hands-free microphone and speaker configuration. The analog baseband
processing
unit 2010 may provide digital-to-analog conversion in one signal direction and
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analog-to-digital conversion in the opposing signal direction. In various
embodiments, at least some of the functionality of the analog baseband
processing
unit 2010 may be provided by digital processing components, for example by the
DSP
2002 or by other central processing units.
[00229] The DSP 2002 may perform modulation/demodulation, coding/decoding,
interleaving/deinterleaving, spreading/despreading, inverse fast Fourier
transforming
(IFFT)/fast Fourier transforming (FFT), cyclic prefix appending/removal, and
other
signal processing functions associated with wireless communications. In an
embodiment, for example in a code division multiple access (CDMA) technology
application, for a transmitter function the DSP 2002 may perform modulation,
coding,
interleaving, and spreading, and for a receiver function the DSP 2002 may
perform
despreading, deinterleaving, decoding, and demodulation. In another
embodiment,
for example in an orthogonal frequency division multiplex access (OFDMA)
technology application, for the transmitter function the DSP 2002 may perform
modulation, coding, interleaving, inverse fast Fourier transforming, and
cyclic prefix
appending, and for a receiver function the DSP 2002 may perform cyclic prefix
removal, fast Fourier transforming, deinterleaving, decoding, and
demodulation. In
other wireless technology applications, yet other signal processing functions
and
combinations of signal processing functions may be performed by the DSP 2002.
[00230] The DSP 2002 may communicate with a wireless network via the analog
baseband processing unit 2010. In some embodiments, the communication may
provide Internet connectivity, enabling a user to gain access to content on
the Internet
and to send and receive e-mail or text messages. The input/output interface
2018
interconnects the DSP 2002 and various memories and interfaces. The memory
2004
and the removable memory card 2020 may provide software and data to configure
the
operation of the DSP 2002. Among the interfaces may be the USB interface 2022
and
the short range wireless communication sub-system 2024. The USB interface 2022
may be used to charge the client node 1902 and may also enable the client node
1902
to function as a peripheral device to exchange information with a personal
computer
or other computer system. The short range wireless communication sub-system
2024
may include an infrared port, a Bluetooth interface, an IEEE 802.11 compliant
wireless interface, or any other short range wireless communication sub-
system,
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which may enable the client node 1902 to communicate wirelessly with other
nearby
client nodes and access nodes.
[00231] The input/output interface 2018 may further connect the DSP 2002 to
the
alert 2026 that, when triggered, causes the client node 1902 to provide a
notice to the
user, for example, by ringing, playing a melody, or vibrating. The alert 2026
may
serve as a mechanism for alerting the user to any of various events such as an
incoming call, a new text message, and an appointment reminder by silently
vibrating,
or by playing a specific pre-assigned melody for a particular caller.
[00232] The keypad 2028 couples to the DSP 2002 via the I/0 interface 2018 to
provide one mechanism for the user to make selections, enter information, and
otherwise provide input to the client node 1902. The keyboard 2028 may be a
full or
reduced alphanumeric keyboard such as QWERTY, Dvorak, AZERTY and sequential
types, or a traditional numeric keypad with alphabet letters associated with a
telephone keypad. The input keys may likewise include a trackwheel, an exit or
escape key, a trackball, and other navigational or functional keys, which may
be
inwardly depressed to provide further input function. Another input mechanism
may
be the LCD 2030, which may include touch screen capability and also display
text
and/or graphics to the user. The LCD controller 2032 couples the DSP 2002 to
the
LCD 2030.
[00233] The CCD camera 2034, if equipped, enables the client node 1902 to take
digital pictures. The DSP 2002 communicates with the CCD camera 2034 via the
camera controller 2036. In another embodiment, a camera operating according to
a
technology other than Charge Coupled Device cameras may be employed. The GPS
sensor 2038 is coupled to the DSP 2002 to decode global positioning system
signals
or other navigational signals, thereby enabling the client node 1902 to
determine its
position. Various other peripherals may also be included to provide additional
functions, such as radio and television reception.
[00234] Figure 21 illustrates a software environment 2102 that may be
implemented by a digital signal processor (DSP). In this embodiment, the DSP
2002
shown in Figure 20 executes an operating system 2104, which provides a
platform
from which the rest of the software operates. The operating system 2104
likewise
provides the client node 1902 hardware with standardized interfaces (e.g.,
drivers)
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that are accessible to application software. The operating system 2104
likewise
comprises application management services (AMS) 2106 that transfer control
between applications running on the client node 1902. Also shown in Figure 21
are a
web browser application 2108, a media player application 2110, and Java
applets
2112. The web browser application 2108 configures the client node 1902 to
operate
as a web browser, allowing a user to enter information into forms and select
links to
retrieve and view web pages. The media player application 2110 configures the
client
node 1902 to retrieve and play audio or audiovisual media. The Java applets
2112
configure the client node 1902 to provide games, utilities, and other
functionality. A
component 2114 may provide functionality described herein. In various
embodiments, the client node 1902, the wireless network node 1908, and the
server
node 1916 shown in Figure 19 may likewise include a processing component that
is
capable of executing instructions related to the actions described above.
[00235] As used herein, the terms "component," "system," and the like are
intended to refer to a computer-related entity, either hardware, a combination
of
hardware and software, software, software in execution. For example, a
component
may be, but is not limited to being, a process running on a processor, a
processor, an
object, an executable, a thread of execution, a program, or a computer. By way
of
illustration, both an application running on a computer and the computer
itself can be
a component. One or more components may reside within a process or thread of
execution and a component may be localized on one computer or distributed
between
two or more computers.
[00236] As likewise used herein, the term "node" broadly refers to a
connection
point, such as a redistribution point or a communication endpoint, of a
communication
environment, such as a network. Accordingly, such nodes refer to an active
electronic
device capable of sending, receiving, or forwarding information over a
communications channel. Examples of such nodes include data circuit-
terminating
equipment (DCE), such as a modem, hub, bridge or switch, and data terminal
equipment (DTE), such as a handset, a printer or a host computer (e.g., a
router,
workstation or server). Examples of local area network (LAN) or wide area
network
(WAN) nodes include computers, packet switches, cable modems, Data Subscriber
Line (DSL) modems, and wireless LAN (WLAN) access points. Examples of Internet
or Intranet nodes include host computers identified by an Internet Protocol
(IP)
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address, bridges and WLAN access points. Likewise, examples of nodes in
cellular
communication include base stations, relays, base station controllers, home
location
registers, Gateway GPRS Support Nodes (GGSN), and Serving GPRS Support Nodes
(S GS N).
[00237] Other examples of nodes include client nodes, server nodes, peer nodes
and access nodes. As used herein, a client node may refer to wireless devices
such as
mobile telephones, smart phones, personal digital assistants (PDAs), handheld
devices, portable computers, tablet computers, and similar devices or other
user
equipment (UE) that has telecommunications capabilities. Such client nodes may
likewise refer to a mobile, wireless device, or conversely, to devices that
have similar
capabilities that are not generally transportable, such as desktop computers,
set-top
boxes, or sensors. Likewise, a server node, as used herein, refers to an
information
processing device (e.g., a host computer), or series of information processing
devices,
that perform information processing requests submitted by other nodes. As
likewise
used herein, a peer node may sometimes serve as client node, and at other
times, a
server node. In a peer-to-peer or overlay network, a node that actively routes
data for
other networked devices as well as itself may be referred to as a supernode.
[00238] An access node, as used herein, refers to a node that provides a
client node
access to a communication environment. Examples of access nodes include
cellular
network base stations and wireless broadband (e.g., WiFi, WiMAX, etc.) access
points, which provide corresponding cell and WLAN coverage areas. As used
herein,
a macrocell is used to generally describe a traditional cellular network cell
coverage
area. Such macrocells are typically found in rural areas, along highways, or
in less
populated areas. As likewise used herein, a microcell refers to a cellular
network cell
with a smaller coverage area than that of a macrocell. Such micro cells are
typically
used in a densely populated urban area. Likewise, as used herein, a picocell
refers to
a cellular network coverage area that is less than that of a microcell. An
example of
the coverage area of a picocell may be a large office, a shopping mall, or a
train
station. A femtocell, as used herein, currently refers to the smallest
commonly
accepted area of cellular network coverage. As an example, the coverage area
of a
femtocell is sufficient for homes or small offices.
[00239] In general, a coverage area of less than two kilometers typically
corresponds to a microcell, 200 meters or less for a picocell, and on the
order of 10
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meters for a femtocell. As likewise used herein, a client node communicating
with an
access node associated with a macrocell is referred to as a "macrocell
client."
Likewise, a client node communicating with an access node associated with a
microcell, picocell, or femtocell is respectively referred to as a "microcell
client,"
"picocell client," or "femtocell client."
[00240] Although the described exemplary embodiments disclosed herein are
described with reference to certain example embodiments, the present
disclosure is
not necessarily limited to the example embodiments which illustrate inventive
aspects
of the present disclosure that are applicable to a wide variety of
authentication
algorithms. Thus, the particular embodiments disclosed above are illustrative
only
and should not be taken as limitations upon the present disclosure, as the
invention
may be modified and practiced in different but equivalent manners apparent to
those
skilled in the art having the benefit of the teachings herein. Accordingly,
the
foregoing description is not intended to limit the invention to the particular
form set
forth, but on the contrary, is intended to cover such alternatives,
modifications and
equivalents as may be included within the spirit and scope of the invention as
defined
by the appended claims so that those skilled in the art should understand that
they can
make various changes, substitutions and alterations without departing from the
spirit
and scope of the invention in its broadest form.
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