U.S. patent application number 14/135296 was filed with the patent office on 2015-01-08 for coordinated interference mitigation and cancelation.
The applicant listed for this patent is Alexei Vladimirovich Davydov, Jong-Kae Fwu, Feng Xue. Invention is credited to Alexei Vladimirovich Davydov, Jong-Kae Fwu, Feng Xue.
Application Number | 20150009903 14/135296 |
Document ID | / |
Family ID | 52132763 |
Filed Date | 2015-01-08 |
United States Patent
Application |
20150009903 |
Kind Code |
A1 |
Xue; Feng ; et al. |
January 8, 2015 |
COORDINATED INTERFERENCE MITIGATION AND CANCELATION
Abstract
A method includes receiving at user equipment an indication of a
subset of scheduling constraints for interference mitigation and
cancelation and performing interference mitigation and cancelation
utilizing the subset of scheduling constraints.
Inventors: |
Xue; Feng; (Redwood City,
CA) ; Fwu; Jong-Kae; (Sunnyvale, CA) ;
Davydov; Alexei Vladimirovich; (Nizhny Novgorod,
RU) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Xue; Feng
Fwu; Jong-Kae
Davydov; Alexei Vladimirovich |
Redwood City
Sunnyvale
Nizhny Novgorod |
CA
CA |
US
US
RU |
|
|
Family ID: |
52132763 |
Appl. No.: |
14/135296 |
Filed: |
December 19, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61843826 |
Jul 8, 2013 |
|
|
|
Current U.S.
Class: |
370/329 |
Current CPC
Class: |
H04W 80/04 20130101;
H04W 28/08 20130101; H04L 5/0048 20130101; H04W 48/16 20130101;
H04L 5/0007 20130101; H04W 8/005 20130101; H04W 72/0413 20130101;
H04L 5/0005 20130101; H04W 56/002 20130101; H04L 5/005 20130101;
H04W 88/02 20130101; H04W 84/042 20130101; H04W 40/246 20130101;
Y02D 30/70 20200801; H04W 84/18 20130101; H04B 15/00 20130101; H04W
28/04 20130101; H04W 72/1215 20130101; H04J 11/00 20130101; H04W
72/082 20130101; H04L 5/0073 20130101; H04W 72/044 20130101 |
Class at
Publication: |
370/329 |
International
Class: |
H04W 72/08 20060101
H04W072/08 |
Claims
1. A device comprising: a transceiver; a processor; and a memory
having instructions for execution by the processor to: receive an
indication of a subset of scheduling constraints for interference
mitigation and cancelation; and perform interference mitigation and
cancelation utilizing the subset of scheduling constraints.
2. The device of claim 1 wherein the indication comprises an index
corresponding to a subset of available scheduling parameters to be
used in the performance of interference mitigation and
cancelation.
3. The device of claim 2 wherein the processor further uses the
index to access a table with multiple indexed sets of subsets of
scheduling constraints corresponding to modulation/transmission
mode/modulation coding scheme/precoding matrix indicator.
4. The device of claim 3 wherein the subset of modulation coding
scheme/resource combinations comprise at least two modulation
coding scheme/resources selected from the group consisting of MCS
(modulation coding scheme), precoding (PMI--precoding matrix
indicator) and frequency-time resources.
5. The device of claim 1 wherein the scheduling constraints specify
that co-scheduled user equipment radio bands are totally
overlapping.
6. The device of claim 5 wherein the scheduling constraints specify
that co-scheduled user equipment radio bands are permitted to start
from a mid-point of a radio band allocation and that the radio
bands are continuous.
7. The device of claim 1 wherein the scheduling constraints specify
that modulation orders of co-scheduled user equipment are within a
limited range.
8. The device of claim 1 wherein the scheduling constraints specify
that transmission modes are within a limited number of
combinations.
9. The device of claim 1 wherein the scheduling constraints specify
that a number of co-scheduled user equipment is limited.
10. A method comprising: receiving at a user equipment an
indication of a subset of scheduling constraints for interference
mitigation and cancelation; and performing interference mitigation
and cancelation utilizing the subset of scheduling constraints.
11. The method of claim 10 wherein the indication comprises an
index corresponding to a subset of available scheduling parameters
to be used in the performance of interference mitigation and
cancelation.
12. The method of claim 11 and further comprising using the index
to access a table with multiple indexed sets of modulation coding
scheme/resource combinations.
13. The method of claim 12 wherein the subset of modulation coding
scheme/resource combinations comprise at least two modulation
coding scheme/resources selected from the group consisting of MCS
(modulation coding scheme), precoding (PMI--precoding matrix
indicator) and frequency-time resources.
14. The method of claim 10 wherein the scheduling constraints for
interference mitigation and cancelation are received by the user
equipment in an interference-cooperation region between neighboring
cells.
15. The method of claim 10 and further comprising: exchanging
information identifying an interference-cooperation region between
neighboring cells; and synchronizing scheduling constraints to
propagate to user equipment in the interference-cooperation
region.
16. The method of claim 15 wherein one scheduling constraint
includes a radio band allocation starting from a specified set of
radio bands.
17. The method of claim 15 wherein one scheduling constraint
includes all user equipment within the interference-cooperation
region using phase-shift keying.
18. A base station comprising: a transceiver; a processor; and a
memory having instructions for execution by the processor to:
identify a subset of scheduling constraints for interference
mitigation and cancelation; and send an indication of the subset of
scheduling constraints to multiple user equipment within a cell of
the base station to enable the user equipment to perform
interference mitigation and cancelation utilizing the subset of
scheduling constraints.
19. The base station of claim 18 and wherein the processor further:
exchanges information identifying an interference-cooperation
region between neighboring cells; and synchronizes scheduling
constraints to propagate to user equipment in the
interference-cooperation region.
20. The base station of claim 15 wherein one subset of scheduling
constraint includes a radio band allocation starting from a
specified set of radio bands and that all user equipment within the
interference-cooperation region use phase-shift keying.
Description
RELATED APPLICATION
[0001] This application claims priority to U.S. Provisional
Application Ser. No. 61/843,826 (entitled ADVANCED WIRELESS
COMMUNICATION SYSTEMS AND TECHNIQUES, filed Jul. 8, 2013) which is
incorporated herein by reference in its entirey.
BRIEF DESCRIPTION OF THE DRAWINGS
[0002] FIG. 1A is a block diagram illustrated intra-cell
interference according to an example embodiment.
[0003] FIG. 1B is a block diagram illustrating inter-cell
interference according to an example embodiment.
[0004] FIG. 2 is a block diagram illustrating limitations on
jointly scheduled UEs according to an example embodiment.
[0005] FIG. 3 is a flowchart illustrating a method of performing
interference mitigation and cancelation according to an example
embodiment.
[0006] FIG. 4 is a table of coordination combinations using a two
bit index according to an example embodiment.
[0007] FIG. 5 is an alternative table of coordination combinations
using a two bit index according to an example embodiment.
[0008] FIG. 6 is a table of coordination combinations using a three
bit index according to an example embodiment.
[0009] FIGS. 7A and 7B are block diagrams illustrating inter-cell
coordination according to an example embodiment.
[0010] FIG. 8 is a block diagram of an example cell station
according to an example embodiment.
BACKGROUND
[0011] Interference is a serious issue in wireless cellular
communications, especially as the cell size gets smaller and user
equipment (UE) density gets higher. It has been shown that
interference mitigation and cancelation (IMC) techniques can be
implemented at the UE side for better throughput and quality of
service (QoS). Since signals from intra-cell or inter-cell UEs are
typically controlled and coded using private scrambling or
allocations, especially in existing releases, an UE can only do
blind IMC by exhaustive search or by linear processing based on
statistics. This entails either high complexity or poor performance
for IMC.
DETAILED DESCRIPTION
[0012] The following detailed description refers to the
accompanying drawings. The same reference numbers may be used in
different drawings to identify the same or similar elements. In the
following description, for purposes of explanation and not
limitation, specific details are set forth such as particular
structures, architectures, interfaces, techniques, etc. in order to
provide a thorough understanding of the various aspects of the
claimed invention. However, it will be apparent to those skilled in
the art having the benefit of the present disclosure that the
various aspects of the invention claimed may be practiced in other
examples that depart from these specific details. In certain
instances, descriptions of well-known devices, circuits, and
methods are omitted so as not to obscure the description of the
present invention with unnecessary detail.
[0013] Interference is a serious issue in wireless cellular
communications, especially as the cell size gets smaller and user
equipment (UE) density gets higher. It has been shown that
interference mitigation and cancelation (IMC) techniques can be
implemented at the UE side for better throughput and quality of
service (QoS). Since signals from intra-cell or inter-cell UEs are
typically controlled and coded using private scrambling or
allocations, a UE can only do blind IMC by exhaustive search or by
linear processing based on statistics. This entails either high
complexity or poor performance for IMC. This is because the number
of possible combinations between resource allocation, PMI
(precoding matrix indicator), and MCS (modulation coding scheme)
etc., is a big number. By sending the UE some side information
about the co-scheduled UE(s) or even cross-cell UEs, one expects to
achieve better IMC result. As a result, example embodiments enable
network-assisted interference cancelation and mitigation.
[0014] In various examples, intra-cell and inter-cell transmissions
on the MCS/resource allocation level are coordinated. An associated
side-information transmission and coding method is provided for
notifying UEs, so that a more efficient and effective IMC is
achieved.
[0015] In one embodiment, scheduling coordination is performed
between MU-MIMO (multiple user multiple-input multiple-output) UEs
in one cell and the coordination across neighboring cells. When the
base station (eNB--evolved node B) schedules a pair or more UEs in
a cell for MU-MIMO, the combinations among MCS, precoding
(PMI--precoding matrix indicator) and frequency-time resources are
limited to a smaller number of possibilities. The combinations are
narrowed and indexed using a few bits, which will be sent to the
UEs as a new type of DCI (downlink control indicator) for better
IMC. In some example embodiments, there may be more than MCS, PMI
and frequency-time resources. One example is power.
[0016] In cross-cell coordination, a slow coordination between
cells is presented which determines a set of frequency-time
resource so that neighboring cells can allocate
interference-suffering UEs in this region. In this so-called
`Interference Coordination Region` (IC-Region), a limited number of
MCS/resource scheduling/PMI etc., combinations are allowed. UEs
scheduled in such region can assume that the interference signal
has limited possible allocations on resource allocation and/or MCS
etc. This allows better IMC and better interference situation.
Several specific options in encoding are also provided.
[0017] FIGS. 1A and 1B illustrate two interference situations.
Intra-cell interference is illustrated at 100 in FIG. 1A, and
involves interference between different UE indicated at 102 and 104
in a single base station (eNB) indicated at 106. Inter-cell
interference is illustrated at 110 in FIG. 1B, and involves
interference between two base stations 112, 114 at one or more UEs
indicated at 116. The sizes of the arrows indicate relative signal
strengths between the UEs and the cell stations. The design for
intra-cell coordination can be considered a special case of the
inter-cell coordination in various examples. Note that limiting
combinations will gain overall in terms of system throughput
especially at cell-edge UEs. This is because these UEs will not
perform well with high MCS orders, fancy scheduling, or complicated
combinations.
[0018] Example mechanisms provide intra-cell and inter-cell
coordination without much overhead. By carefully choosing the
limited number of combinations, a better trade-off is achieved
between interference-cancelation performance of cell-edge UEs and
overall system throughput.
[0019] In LTE, scheduling of a UE's transmission has many
parameters such as modulation order (e.g. QPSK/16QAM/64QAM), MCS
(index of the modulation/coding combinations), PMI, resource
allocations, transmission mode, layers/ranks etc. We call this set
of parameters the `scheduling parameters`. This creates a big
search space for any UE that tries to do interference cancelation
or mitigation in a fine way.
[0020] In one example, a scheduling method for the eNB limits the
number of possible combinations between co-scheduled UEs (e.g.
MU-MIMO or cross-cell). This may be referred to as a subset of
scheduling constraints, which by definition, contains fewer
constraints than are normally available for use in performing
interference-cancelation mitigation. In one embodiment, the
scheduling constraint is on modulation/TM (transmission
mode)/MCS/PMI. The coordinated parameters may be within a limited
boundary of each other (as compared to the number of possibilities
if there is no such coordination).
[0021] A UE may be notified by its eNB that it is under such a
co-scheduling coordination, by special signaling. A new DCI format
with dedicated K bits (e.g. 2 or 3) is used by the eNB to indicate
the coordination pattern, i.e. which limitations are to be
enforced. This new DCI may be changed at a sub-frame level.
[0022] At a high-level, such as RRC (radio resource control), with
a slower period, the mapping between the bits and the coordination
patterns can be changed. Neighboring cells can be coordinated over
a backhaul (e.g. X2) in a much slower frequency for coordinating
scheduling towards a better IMC performance. Neighboring cells may
agree on a special resource region (IC-region) on the resource grid
(e.g. a set of RBs across certain subframes). UEs scheduled in this
region may have a very limited number of possible combinations of
scheduling parameters. In a further example, an eNB can provide UEs
in the IC-Region more information by using a new DCI as in the
intra-cell coordination case.
[0023] Regarding to the possible combinations, once a UE (say UE0)
is notified that it is scheduled with interference-coordination,
the following limitation on the jointly-scheduled UEs, as
illustrated at 200 in FIG. 2, is enforced:
[0024] 1) Resource allocation of any co-scheduled UEs 210, 215 have
only a limited number of starting points and scheduling patterns.
For example, one option is to assume that co-scheduled UE RBs
(radio bands) can only be totally overlapping or start, or in the
case of UEs 220, 225 from the mid-point 230 of UE0's RB allocation,
and the RBs must be continuous;
[0025] 2) Modulation orders of co-scheduled UEs are within a
limited range, e.g. 0 (equal order) or 1. MCS orders can be assumed
to be within a certain range, which can be inferred based on the
new DCI message;
[0026] 3) Transmission modes are within a limited number of
combinations.
[0027] 4) The number of co-scheduled layers should be limited. New
DCI can specify further limits on the number. E.g. no more than 2
or 4. This also applies to the number of co-scheduled UEs.
[0028] In intra-cell design, the eNB has a set of coordination
modes, say Model, . . . , ModeJ. Each mode corresponds to a table
of K items, with each item being represented by an index. Each item
limits the scheduling options of the joint-scheduled UEs. The
coordinated properties include: RB allocation, modulation order,
TM, number of co-scheduled UEs, number of layers, etc.
[0029] A method 300 of performing interference mitigation and
cancelation utilizing various resource allocation modes is
illustrated in FIG. 3. At 310, RRC signaling may be used to specify
which mode is in effect. At 315, in a control instruction (PDCCH),
the coordination is instructed to the UE by letting it know the
item's index. At 320, based on the `mode` and `item index`, the UE
limits the co-scheduling options, which helps its interference
mitigation in decoding. At 325, a UE can typically assume that all
its co-scheduled UEs don't use 64QAM. (Because 64QAM is the finest
modulation order and like random Gaussian noise already.)
[0030] DCI may be used in two different options. In a first option,
a private DCI is sent to a co-scheduled UE as identified by the
eNB. This option allows a legacy UE who does not understand the new
DCI to be co-scheduled. In a second option, a common DCI is
multi-casted to all co-scheduled UEs. This control channel may be
scrambled and coded using sequences known to all these UEs.
[0031] Several design options may utilize at least 2 or 3 bits
indicating the coordination combinations. In one example, two-bit
information is sent. Each such information indicates certain
limitations on possible combinations. The emphasis is the case when
the co-scheduled UEs have similar scheduling setup.
[0032] In one specific example illustrated in table form in FIG. 4
at 400, it is assumed that UE0 is the UE that received this new
DCI. M(0) is the modulation order of UE0, and M(k) is for the
coordinated UE(k). An index column 410 shows four entries, 0, 1, 2,
and 3, corresponding to a two bit index. RB allocation is shown at
415. The RB allocation may change in the middle or switch once at a
mid-point in this example. Modulation order is shown at 420, and
may be the same, or vary between M(0)-1 and M(0)+1 as illustrated.
A TM (Transmission mode) 425 is shown the same as UE0 for each UE,
as are the RS port positions at 430. A number of co-scheduled UEs
in column 435 varies between 1 and less than or equal to 4. A
number of co-scheduled ranks at 440 may also vary between 1 and
less than or equal to 4.
[0033] In a further option illustrated in table form at 500 in FIG.
5 a UE can assume that no 64QAM is used. Table 500 uses the same
reference numbers as table 400 where the columns are the same. In
addition, a power difference of .times.dB is indicated at 510 and
is a threshold number. Not much use of side information is made if
64QAM is utilized.
[0034] In a still further option, coordination between
rank/RB/modulation/TM/#UEs is utilized as indicated at table 600 in
FIG. 6. The index 610 in this example is a three bit index having
corresponding Arabic numbers 0 through 7, for a total of up to 8
entries. RB allocation is illustrated at 615. Modulation order is
shown at 620 and may be the same as UE0, the same as UE0 on all
layers, vary between M(0)-1 and M(0)+1, equal to M(0)-1 or M(0)+1,
M(k)=M(0)+1, M(k)=M(0)-1 or M(0), M(k) less than or equal to M(0)+1
in various examples. In this example, the only difference between
index 0 and index 1 is that the latter allows two co-scheduled
ranks. The term "all layers" means that both layers' scheduling is
subject to the same constraint. TM is indicated at 625 and may be
the same as UE0 or legacy, the same as UE0 or legacy on all layers.
PR port positions are indicated at 630 and may be the same as UE0
or the same as UE0 on all layers. A number of co-scheduled UEs is
indicated at 635 and may vary between 1 and 4, with specific
examples illustrated as 1, 2, and less than or equal to 4. Finally,
the number of co-scheduled ranks at 640 may also range from 1 to 4,
with specific examples illustrated as 1, 2, and less than or equal
to 4.
[0035] A further option is that UE can assume that no 64QAM is
used. Besides the above combinations, the following side
information can be sent for better information compression. Side
information 1: Total number of UEs/Ranks scheduled. Side
information 2: maximum variations of certain parameters between the
UEs. E.g. |ModulationOrder(i)-ModulationOrder(j)|<=1, excluding
64QAM; or |MCS(i)-MCS(j)|<=3.
[0036] Inter-cell coordination may also be performed. The basic
structure and steps are illustrated in FIGS. 7A at 700 and in 7B.
Neighboring cells indicated at 710 and 715 exchange over X2 (or
other backhaul channel) for coordinating IMC. Over X2, a dedicated
resource region A at 720 (freq+time) is designated as
`interference-cooperation region`(IC-region). In this IC-region
720, each cell's scheduling can be implicitly or easily derivable
by neighbors. Over a fixed period, e.g. 200 ms, the neighboring
cells 710, 715 synchronize again on IC-region A 720 and the
derivation mechanism (i.e. the scheduling constraints) for
scheduling in A.
[0037] Scheduling alignment in IC-region 720: For a UE that gets
scheduled in the IC-region, it can infer that the scheduling
coordination takes effect. Parameters under coordination are
similar as in the intra-cell MU-MIMO case.
[0038] There are many options of limiting the possible coordination
combinations within IC-region. Several options are presented here,
including all the UEs in region A can only use QPSK (phase-shift
keying). In a further option, a UE's RB allocation starts from a
specified set of RBs (e.g. continuous) and/or with fixed length
(e.g 3/6/9RBs). This helps the neighbor UEs in blind interference
cancelation and mitigation. In yet a further option, for each RB
block, its transmission is fixed to be say RANK1, 16QAM, a very
limited number of combinations.
[0039] FIG. 8 is a block diagram of a specifically programmed
computer system to act as one or more different types of cell
stations, including user equipment, small cell stations and macro
stations. The system may be used to implement one or more methods
according to the examples described. In the embodiment shown in
FIG. 8, a hardware and operating environment is provided to enable
the computer system to execute one or more methods and functions
that are described herein. In some embodiments, the system may be a
small cell station, macro cell station, smart phone, tablet, or
other networked device that can provide access and wireless
networking capabilities to one or more devices. Such devices need
not have all the components included in FIG. 8.
[0040] FIG. 8 illustrates a functional block diagram of a cell
station 800 in accordance with some embodiments. Cell station 800
may be suitable for use as a small cell station, macro cell
station, or user equipment, such as a wireless cell phone, tablet
or other computer. The cell station 800 may include physical layer
circuitry 802 for transmitting and receiving signals to and from
eNBs using one or more antennas 801. Cell station 800 may also
include processing circuitry 804 that may include, among other
things a channel estimator. Cell station 800 may also include
memory 806. The processing circuitry may be configured to determine
several different feedback values discussed below for transmission
to the eNB. The processing circuitry may also include a media
access control (MAC) layer.
[0041] In some embodiments, the cell station 800 may include one or
more of a keyboard, a display, a non-volatile memory port, multiple
antennas, a graphics processor, an application processor, speakers,
and other mobile device elements. The display may be an LCD screen
including a touch screen.
[0042] The one or more antennas 801 utilized by the cell station
800 may comprise one or more directional or omnidirectional
antennas, including, for example, dipole antennas, monopole
antennas, patch antennas, loop antennas, microstrip antennas or
other types of antennas suitable for transmission of RF signals. In
some embodiments, instead of two or more antennas, a single antenna
with multiple apertures may be used. In these embodiments, each
aperture may be considered a separate antenna. In some
multiple-input multiple-output (MIMO) embodiments, the antennas may
be effectively separated to take advantage of spatial diversity and
the different channel characteristics that may result between each
of antennas and the antennas of a transmitting station. In some
MIMO embodiments, the antennas may be separated by up to 1/10 of a
wavelength or more.
[0043] Although the cell station 800 is illustrated as having
several separate functional elements, one or more of the functional
elements may be combined and may be implemented by combinations of
software-configured elements, such as processing elements including
digital signal processors (DSPs), and/or other hardware elements.
For example, some elements may comprise one or more
microprocessors, DSPs, application specific integrated circuits
(ASICs), radio-frequency integrated circuits (RFICs) and
combinations of various hardware and logic circuitry for performing
at least the functions described herein. In some embodiments, the
functional elements may refer to one or more processes operating on
one or more processing elements.
[0044] Embodiments may be implemented in one or a combination of
hardware, firmware and software. Embodiments may also be
implemented as instructions stored on a computer-readable storage
medium, which may be read and executed by at least one processor to
perform the operations described herein. A computer-readable
storage medium may include any non-transitory mechanism for storing
information in a form readable by a machine (e.g., a computer). For
example, a computer-readable storage medium may include read-only
memory (ROM), random-access memory (RAM), magnetic disk storage
media, optical storage media, flash-memory devices, and other
storage devices and media. In these embodiments, one or more
processors of the cell station 800 may be configured with the
instructions to perform the operations described herein.
[0045] In some embodiments, the cell station 800 may be configured
to receive OFDM communication signals over a multicarrier
communication channel in accordance with an OFDMA communication
technique. The OFDM signals may comprise a plurality of orthogonal
subcarriers. In some broadband multicarrier embodiments, evolved
node Bs (NBs) may be part of a broadband wireless access (BWA)
network communication network, such as a Worldwide Interoperability
for Microwave Access (WiMAX) communication network or a 3rd
Generation Partnership Project (3GPP) Universal Terrestrial Radio
Access Network (UTRAN) Long-Term-Evolution (LTE) or a
Long-Term-Evolution (LTE) communication network, although the scope
of the invention is not limited in this respect. In these broadband
multicarrier embodiments, the cell station 800 and the eNBs may be
configured to communicate in accordance with an orthogonal
frequency division multiple access (OFDMA) technique. The UTRAN LTE
standards include the 3rd Generation Partnership Project (3GPP)
standards for UTRAN-LTE, release 8, March 2008, and release 10,
December 2010, including variations and evolutions thereof.
[0046] In some LTE embodiments, the basic unit of the wireless
resource is the Physical Resource Block (PRB). The PRB may comprise
12 sub-carriers in the frequency domain.times.0.5 ms in the time
domain. The PRBs may be allocated in pairs (in the time domain). In
these embodiments, the PRB may comprise a plurality of resource
elements (REs). A RE may comprise one sub-carrier.times.one
symbol.
[0047] Two types of reference signals may be transmitted by an eNB
including demodulation reference signals (DM-RS), channel state
information reference signals (CIS-RS) and/or a common reference
signal (CRS). The DM-RS may be used by the UE for data
demodulation. The reference signals may be transmitted in
predetermined PRBs. In some embodiments, the OFDMA technique may be
either a frequency domain duplexing (FDD) technique that uses
different uplink and downlink spectrum or a time-domain duplexing
(TDD) technique that uses the same spectrum for uplink and
downlink.
[0048] In some other embodiments, the cell station 800 and the eNBs
may be configured to communicate signals that were transmitted
using one or more other modulation techniques such as spread
spectrum modulation (e.g., direct sequence code division multiple
access (DS-CDMA) and/or frequency hopping code division multiple
access (FH-CDMA)), time-division multiplexing (TDM) modulation,
and/or frequency-division multiplexing (FDM) modulation, although
the scope of the embodiments is not limited in this respect.
[0049] In some embodiments, the cell station 800 may be part of a
portable wireless communication device, such as a personal digital
assistant (PDA), a laptop or portable computer with wireless
communication capability, a web tablet, a wireless telephone, a
wireless headset, a pager, an instant messaging device, a digital
camera, an access point, a television, a medical device (e.g., a
heart rate monitor, a blood pressure monitor, etc.), or other
device that may receive and/or transmit information wirelessly.
[0050] In some LTE embodiments, the cell station 800 may calculate
several different feedback values which may be used to perform
channel adaption for closed-loop spatial multiplexing transmission
mode. These feedback values may include a channel-quality indicator
(CQI), a rank indicator (RI) and a precoding matrix indicator
(PMI). By the CQI, the transmitter selects one of several
modulation alphabets and code rate combinations. The RI informs the
transmitter about the number of useful transmission layers for the
current MIMO channel, and the PMI indicates the codebook index of
the precoding matrix (depending on the number of transmit antennas)
that is applied at the transmitter. The code rate used by the eNB
may be based on the CQI. The PMI may be a vector that is calculated
by the cell station and reported to the eNB. In some embodiments,
the cell station may transmit a physical uplink control channel
(PUCCH) of format 2, 2a or 2b containing the CQI/PMI or RI.
[0051] In these embodiments, the CQI may be an indication of the
downlink mobile radio channel quality as experienced by the cell
station 800. The CQI allows the cell station 800 to propose to an
eNB an optimum modulation scheme and coding rate to use for a given
radio link quality so that the resulting transport block error rate
would not exceed a certain value, such as 10%. In some embodiments,
the cell station may report a wideband CQI value which refers to
the channel quality of the system bandwidth. The cell station may
also report a sub-band CQI value per sub-band of a certain number
of resource blocks which may be configured by higher layers. The
full set of sub-bands may cover the system bandwidth. In case of
spatial multiplexing, a CQI per code word may be reported.
[0052] In some embodiments, the PMI may indicate an optimum
precoding matrix to be used by the eNB for a given radio condition.
The PMI value refers to the codebook table. The network configures
the number of resource blocks that are represented by a PMI report.
In some embodiments, to cover the system bandwidth, multiple PMI
reports may be provided. PMI reports may also be provided for
closed loop spatial multiplexing, multi-user MIMO and closed-loop
rank 1 precoding MIMO modes.
[0053] In some cooperating multipoint (CoMP) embodiments, the
network may be configured for joint transmissions to a cell station
in which two or more cooperating/coordinating points, such as
remote-radio heads (RRHs) transmit jointly. In these embodiments,
the joint transmissions may be MIMO transmissions and the
cooperating points are configured to perform joint beamforming.
LTE Channel Estimation
[0054] To facilitate the estimation of the channel characteristics
LTE uses cell specific reference signals (i.e., pilot symbols)
inserted in both time and frequency. These pilot symbols provide an
estimate of the channel at given locations within a subframe.
Through interpolation it is possible to estimate the channel across
an arbitrary number of subframes. The pilot symbols in LTE are
assigned positions within a subframe depending on the eNodeB cell
identification number and which transmit antenna is being used, as
shown in the figure below. The unique positioning of the pilots
ensures that they do not interfere with one another and can be used
to provide a reliable estimate of the complex gains imparted onto
each resource element within the transmitted grid by the
propagation channel.
[0055] To minimize the effects of noise on the pilot estimates, the
least square estimates are averaged using an averaging window. This
simple method produces a substantial reduction in the level of
noise found on the pilots. There are two pilot symbol averaging
methods available.
[0056] Time averaging is performed across each pilot symbol
carrying subcarrier, resulting in a column vector containing an
average amplitude and phase for each reference signal carrying
subcarrier.
[0057] All the pilot symbols found in a subcarrier are time
averaged across all OFDM symbols, resulting in a column vector
containing the average for each reference signal subcarrier, The
averages of the pilot symbol subcarriers are then frequency
averaged using a moving window of maximum size.
[0058] In some embodiments, The PSS and SSS provide the cell
station with its physical layer identity within the cell. The
signals may also provide frequency and time synchronization within
the cell. The PSS may be constructed from Zadoff-Chu (ZC) sequences
and the length of the sequence may be predetermined (e.g., 62) in
the frequency domain. The SSS uses two interleaved sequences (i.e.,
maximum length sequences (MLS), SRGsequences or m-sequences) which
are of a predetermined length (e.g., 31). The SSS may be scrambled
with the PSS sequences that determine physical layer ID. One
purpose of the SSS is to provide the cell station with information
about the cell ID, frame timing properties and the cyclic prefix
(CP) length. The cell station may also be informed whether to use
TDD or FD. In FDD, the PSS may be located in the last OFDM symbol
in first and eleventh slot of the frame, followed by the SSS in the
next symbol. In TDD, the PSS may be sent in the third symbol of the
3rd and 13th slots while SSS may be transmitted three symbols
earlier. The PSS provided the cell station with information about
to which of the three groups of physical layers the cell belongs to
(3 groups of 168 physical layers). One of 168 SSS sequences may be
decoded right after PSS and defines the cell group identity
directly.
[0059] In some embodiments, the cell station may be configured in
one of 8 "transmission modes" for PDSCH reception:; Mode 1: Single
antenna port, port 0; Mode 2: Transmit diversity; Mode 3:
Large-delay CDD; Mode 4: Closed-loop spatial multiplexing; Mode 5:
MU-MIMO; Mode 6: Closed-loop spatial multiplexing, single layer;
Mode 7: Single antenna port, cell station-specific RS (port 5);
Mode 8 (new in Rel-9): Single or dual-layer transmission with cell
station -specific RS (ports 7 and/or 8). The CSI-RS are used by the
cell station for channel estimates (i.e., CQI measurements). In
some embodiments, the CSI-RS are transmitted periodically in
particular antenna ports (up to eight transmit antenna ports) at
different subcarrier frequencies (assigned to the cell station) for
use in estimating a MIMO channel. In some embodiments, a cell
station-specific demodulation reference signal (e.g., a DM-RS) may
be precoded in the same way as the data when non-codebook-based
precoding is applied.
EXAMPLES
[0060] 1. An example device comprising: [0061] a transceiver;
[0062] a processor; and [0063] a memory having instructions for
execution by the processor to: [0064] receive an indication of a
subset of scheduling constraints for interference mitigation and
cancelation; and [0065] perform interference mitigation and
cancelation utilizing the subset of scheduling constraints.
[0066] 2. The example device of example 1 wherein the indication
comprises an index corresponding to a subset of available
scheduling parameters to be used in the performance of interference
mitigation and cancelation.
[0067] 3. The example device of example 2 wherein the processor
further uses the index to access a table with multiple indexed sets
of modulation coding scheme/resource combinations.
[0068] 4. The example device of example 3 wherein the subset of
modulation coding scheme/resource combinations comprise at least
two modulation coding scheme/resources selected from the group
consisting of MCS (modulation coding scheme), precoding
(PMI--precoding matrix indicator) and frequency-time resources.
[0069] 5. The example device of example 1 wherein the scheduling
constraints specify that co-scheduled user equipment radio bands
are totally overlapping.
[0070] 6. The example device of example 5 wherein the scheduling
constraints specify that co-scheduled user equipment radio bands
are permitted to start from a mid-point of a radio band allocation
and that the radio bands are continuous.
[0071] 7. The example device of example 1 wherein the scheduling
constraints specify that modulation orders of co-scheduled user
equipment are within a limited range.
[0072] 8. The example device of example 1 wherein the scheduling
constraints specify that transmission modes are within a limited
number of combinations.
[0073] 9. The example device of example 1 wherein the scheduling
constraints specify that a number of co-scheduled user equipment is
limited.
[0074] 10. An example method comprising: [0075] receiving at a user
equipment an indication of a subset of scheduling constraints for
interference mitigation and cancelation; and performing
interference mitigation and cancelation utilizing the subset of
scheduling constraints.
[0076] 11. The example method of example 10 wherein the indication
comprises an index corresponding to a subset of available
scheduling parameters to be used in the performance of interference
mitigation and cancelation.
[0077] 12. The example method of example 11 and further comprising
using the index to access a table with multiple indexed sets of
modulation coding scheme/resource combinations.
[0078] 13. The example method of example 12 wherein the subset of
modulation coding scheme/resource combinations comprise at least
two modulation coding scheme/resources selected from the group
consisting of MCS (modulation coding scheme), precoding
(PMI--precoding matrix indicator) and frequency-time resources.
[0079] 14. The example method of example 10 wherein the scheduling
constraints for interference mitigation and cancelation are
received by the user equipment in an interference-cooperation
region between neighboring cells.
[0080] 15. The example method of example 10 and further comprising:
[0081] exchanging information identifying an
interference-cooperation region between neighboring cells; and
[0082] synchronizing scheduling constraints to propagate to user
equipment in the interference-cooperation region.
[0083] 16. The example method of example 15 wherein one scheduling
constraint includes a radio band allocation starting from a
specified set of radio bands.
[0084] 17. The example method of example 15 wherein one scheduling
constraint includes all user equipment within the
interference-cooperation region using phase-shift keying.
[0085] 18. An example base station comprising: [0086] a
transceiver; [0087] a processor; and [0088] a memory having
instructions for execution by the processor to: [0089] identify a
subset of scheduling constraints for interference mitigation and
cancelation; and [0090] send an indication of the subset of
scheduling constraints to multiple user equipment within a cell of
the base station to enable the user equipment to perform
interference mitigation and cancelation utilizing the subset of
scheduling constraints.
[0091] 19. The example base station of example 18 and wherein the
processor further: [0092] exchanges information identifying an
interference-cooperation region between neighboring cells; and
[0093] synchronizes scheduling constraints to propagate to user
equipment in the interference-cooperation region.
[0094] 20. The example base station of example 15 wherein one
subset of scheduling constraint includes a radio band allocation
starting from a specified set of radio bands and that all user
equipment within the interference-cooperation region use
phase-shift keying.
[0095] In various embodiments, the scheduling constraint is on
modulation/TM/MCS/PMI. In one example, the coordinated parameters
are within a limited boundary of each other (as compared to the
number of possibilities if there is no such coordination).
[0096] 2-3 bits may be used to index into tables to limit the
difference between co-scheduled UEs. The tables may be used to
select a combination to limit the possible combinations between
co-scheduled UEs (or the UEs scheduled on similar resources in a
neighboring cell). So that an UE can figure out easily the
scheduling combinations of the interfering signals. The set of
tables may be used to limit the combination, with emphasis on
modulation order, transmission mode and power difference, etc. Note
the tables themselves have certain flexibility to accommodate
changes. For example, in FIG. 5 ".times.dB" is used. Coordination
may also be done across cells on an interference coordination
region.
[0097] The foregoing description of one or more implementations
provides illustration and description, but is not intended to be
exhaustive or to limit the scope of the invention to the precise
form disclosed. Modifications and variations are possible in light
of the above teachings or may be acquired from practice of various
implementations of the invention.
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