U.S. patent application number 14/202913 was filed with the patent office on 2015-08-27 for scheduling in a cellular communication system using a large excess number of base station antennas.
This patent application is currently assigned to Broadcom Corporation. The applicant listed for this patent is Broadcom Corporation. Invention is credited to Paulraj AROGYASWAMI.
Application Number | 20150245370 14/202913 |
Document ID | / |
Family ID | 53883601 |
Filed Date | 2015-08-27 |
United States Patent
Application |
20150245370 |
Kind Code |
A1 |
AROGYASWAMI; Paulraj |
August 27, 2015 |
Scheduling in a Cellular Communication System Using a Large Excess
Number of Base Station Antennas
Abstract
The present disclosure is directed to a system and method for
selecting a sub-group of user terminals (UTs) among a group of UTs
served by a sector of a cellular network to schedule independent
data streams for transmission to over the same time-frequency
interval. In one embodiment, the sub-group of UTs is selected to
limit inter-user interference among the sub-group of UTs. In
another embodiment, the sub-group of UTs is selected to limit
inter-user interference experienced by a UT that is at or near the
boundary of the sector that serves the sub-group of UTs.
Inventors: |
AROGYASWAMI; Paulraj;
(Stanford, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Broadcom Corporation |
Irvine |
CA |
US |
|
|
Assignee: |
Broadcom Corporation
Irvine
CA
|
Family ID: |
53883601 |
Appl. No.: |
14/202913 |
Filed: |
March 10, 2014 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
61943022 |
Feb 21, 2014 |
|
|
|
Current U.S.
Class: |
370/330 |
Current CPC
Class: |
H04W 16/14 20130101;
H04B 7/024 20130101; H04W 72/121 20130101; H04B 7/0452 20130101;
H04W 72/1226 20130101; H04W 16/24 20130101 |
International
Class: |
H04W 72/12 20060101
H04W072/12; H04B 7/02 20060101 H04B007/02; H04W 16/14 20060101
H04W016/14 |
Claims
1. A method, comprising: selecting a subgroup of user terminals
(UTs) from among a group of UTs served by a first sector to limit
inter-user interference at an edge UT served by a second sector;
scheduling, for each UT in the subgroup of UTs, a different data
stream for transmission over a same time-frequency interval; and
precoding the different data streams to produce precoded data
streams for transmission over the same time-frequency interval by
more antennas than the number of precoded data streams.
2. The method of claim 1, wherein selecting the subgroup of UTs
further comprises: selecting the subgroup of UTs based on a
location of each UT in the group of UTs and a location of the edge
UT.
3. The method of claim 1, wherein selecting the subgroup of UTs
further comprises: selecting the subgroup of UTs based on a message
received from the second sector.
4. The method of claim 3, wherein the message is transmitted from
the second sector to the first sector.
5. The method of claim 3, wherein the message is transmitted from a
cell of the first sector to a cell of the second sector.
6. The method of claim 3, wherein the message comprises a location
of the edge UT.
7. The method of claim 3, wherein the message comprises a time that
a data stream is scheduled to be transmitted to the edge UT.
8. The method of claim 1, wherein the first sector and the second
sector are in a same cell.
9. The method of claim 1, wherein the first sector and the second
sector are in different cells.
10. The method of claim 1, wherein the edge UT is closest to an
edge of the second sector that is adjacent to an edge of the first
sector.
11. A system, comprising: a scheduler configured to schedule, for
each UT in a subgroup of UTs, a different data stream for
transmission over a same time-frequency interval, wherein the
scheduler selects the subgroup of UTs from among a group of UTs
served by a first sector to limit inter-user interference at an
edge UT served by a second sector; and a precoder configured to
precode the different data streams to produce precoded data streams
for transmission over the same time-frequency interval by more
antennas than the number of precoded data streams.
12. The system of claim 11, wherein the scheduler is further
configured to select the subgroup of UTs from among the group of
UTs served by the first sector based on a location of each UT in
the group of UTs and a location of the edge UT.
13. The system of claim 11, wherein the scheduler is further
configured to select the subgroup of UTs from among the group of
UTs served by the first sector based on a message received from the
second sector.
14. The system of claim 13, wherein the message is transmitted from
the second sector to the first sector.
15. The system of claim 13, wherein the message is transmitted from
a cell of the first sector to a cell of the second sector.
16. The system of claim 13,--wherein the message comprises a time
that a data stream is scheduled to be transmitted to the edge
UT.
17. A method, comprising: selecting a subgroup of user terminals
(UTs) from among a group of UTs served by a first sector based on a
location of a UT in the group of UTs served by the first sector to
limit inter-user interference at an edge UT served by a second
sector; scheduling, for each UT in the subgroup of UTs, a different
data stream for transmission over a same time-frequency interval;
preceding the different data streams to produce precoded data
streams for transmission over the same time-frequency interval by
more antennas than the number of precoded data streams.
18. The method of claim 17, wherein selecting the subgroup of UTs
further comprises: selecting the subgroup of UTs based on a message
received from the second sector.
19. The method of claim 18, wherein the message comprises a
location of the edge UT.
20. The method of claim 18, wherein the message comprises a time
that a data stream is scheduled to be transmitted to the edge UT.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Patent Application No. 61/943,022, filed Feb. 21, 2014, which is
incorporated by reference herein.
TECHNICAL FIELD
[0002] This application relates generally to scheduling in a
cellular communication system that uses a large excess number of
base station antennas.
BACKGROUND
[0003] In a cellular communication system, multiple antennas at a
base station (BS) and multiple antennas at one or more user
terminals (UTs) served by the BS allow two or more independent data
streams to be transmitted from the BS to the UT(s) over the same
time-frequency interval. The specific transmission technique that
makes this possible is referred to as spatial multiplexing. In
general, spatial multiplexing is a multiple-input, multiple-output
(MIMO) transmission technique that uses the different "paths" or
channels that exist between the multiple antennas at the BS and the
multiple antennas at the one or more UTs to spatially multiplex the
independent data streams over the same time-frequency interval.
When one UT is served two or more independent data streams by the
BS over the same time-frequency interval, the system is said to be
performing single-user MIMO (SU-MIMO), and when multiple UTs are
each served one or more independent data streams by the BS over the
same time-frequency interval, the system is said to be performing
multi-user MIMO (MU-MIMO).
[0004] The number of independent data streams that can be
transmitted over the same time-frequency interval can be shown to
be limited by the lesser of the number of antennas at the BS and
the total number of antennas at the one or more UTs. A further
limitation on the number of independent data streams that can be
transmitted over the same time-frequency interval results from
interference between the independent data streams or what is
referred to as inter-user interference in the MU-MIMO context.
[0005] In T. L. Marzetta, "Noncooperative Cellular Wireless with
Unlimited Numbers of Base Station Antennas," IEEE Transactions on
Wireless Communications, vol. 9, no. 11, pp. 3590-3600, Nov. 2010
[Marzetta], a concept referred to as "massive MIMO" was introduced.
In general terms, massive MIMO refers to a communication system
that has a large number of excess antennas available at the BS over
the number of independent data streams to be transmitted over the
same time-frequency interval. The excess antennas are used to
reduce inter-user interference by further focusing the energy of
each independent data stream into ever-narrower regions of space.
This is done by appropriately shaping the independent data streams
so that the wave fronts emitted by the available antennas for each
of the independent data streams add up constructively at the
location of the UT intended to receive the independent data stream
and destructively everywhere else (or at least everywhere else
where another UT is intended to receive a different independent
data stream over the same time-frequency interval). The process of
shaping the independent data streams at the BS is known as
precoding.
[0006] Although inter-user interference can be reduced using the
concept of massive MIMO, for a practical number of excess antennas
at the BS, inter-user interference can still affect downlink data
transmissions without proper scheduling.
BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES
[0007] The accompanying drawings, which are incorporated herein and
form a part of the specification, illustrate the embodiments of the
present disclosure and, together with the description, further
serve to explain the principles of the embodiments and to enable a
person skilled in the pertinent art to make and use the
embodiments.
[0008] FIG. 1 illustrates an exemplary cellular network in which
embodiments of the present disclosure can be implemented.
[0009] FIG. 2 illustrates a block diagram of an exemplary BS in
accordance with embodiments of the present disclosure.
[0010] FIG. 3A illustrates an exemplary scenario in which
scheduling can be used to reduce inter-user interference in
accordance with embodiments of the present disclosure.
[0011] FIG. 3B illustrates another exemplary scenario in which
scheduling can be used to reduce inter-user interference in
accordance with embodiments of the present disclosure.
[0012] FIG. 3C illustrates another exemplary scenario in which
scheduling can be used to reduce inter-user interference in
accordance with embodiments of the present disclosure.
[0013] FIG. 3D illustrates another exemplary scenario in which
scheduling can be used to reduce inter-user interference in
accordance with embodiments of the present disclosure.
[0014] FIG. 4 illustrates a flowchart of a method for scheduling in
a cellular communication system that uses a large number of excess
transmit antennas in accordance with embodiments of the present
disclosure.
[0015] FIG. 5 illustrates a block diagram of an example computer
system that can be used to implement aspects of the present
disclosure.
[0016] The embodiments of the present disclosure will be described
with reference to the accompanying drawings. The drawing in which
an element first appears is typically indicated by the leftmost
digit(s) in the corresponding reference number.
DETAILED DESCRIPTION
[0017] In the following description, numerous specific details are
set forth in order to provide a thorough understanding of the
embodiments of the present disclosure. However, it will be apparent
to those skilled in the art that the embodiments, including
structures, systems, and methods, may be practiced without these
specific details. The description and representation herein are the
common means used by those experienced or skilled in the art to
most effectively convey the substance of their work to others
skilled in the art. In other instances, well-known methods,
procedures, components, and circuitry have not been described in
detail to avoid unnecessarily obscuring aspects of the
disclosure.
[0018] References in the specification to "one embodiment," "an
embodiment," "an example embodiment," etc., indicate that the
embodiment described may include a particular feature, structure,
or characteristic, but every embodiment may not necessarily include
the particular feature, structure, or characteristic. Moreover,
such phrases are not necessarily referring to the same embodiment.
Further, when a particular feature, structure, or characteristic is
described in connection with an embodiment, it is submitted that it
is within the knowledge of one skilled in the art to affect such
feature, structure, or characteristic in connection with other
embodiments whether or not explicitly described.
[0019] For purposes of this discussion, the term "module" shall be
understood to include software, firmware, or hardware (such as one
or more circuits, microchips, processors, and/or devices), or any
combination thereof. In addition, it will be understood that each
module can include one, or more than one, component within an
actual device, and each component that forms a part of the
described module can function either cooperatively or independently
of any other component forming a part of the module. Conversely,
multiple modules described herein can represent a single component
within an actual device. Further, components within a module can be
in a single device or distributed among multiple devices in a wired
or wireless manner.
I. Overview
[0020] The present disclosure is directed to a system and method
for selecting a sub-group of UTs among a group of UTs served by a
sector of a cellular network to schedule independent data streams
for transmission to over the same time-frequency interval. In one
embodiment, the sub-group of UTs is selected to limit inter-user
interference among the sub-group of UTs. In another embodiment, the
sub-group of UTs is selected to limit inter-user interference
experienced by a UT that is at or near the boundary of a sector
that is adjacent to the sector that serves the sub-group of UTs.
These and other features of the system and method of the present
disclosure are described further below.
II. System and Method for Scheduling Downlink Transmissions
[0021] FIG. 1 illustrates an exemplary cellular network 100 in
which embodiments of the present disclosure can be implemented.
Cellular network 100 is divided up into cells 102-106 that are each
served by a respective base station (BS) 108-112. Each cell 102-106
can, in-turn, be further divided up into sectors. For example, as
shown in FIG. 1, cell 102 is divided up into three sectors 102-1,
102-2, and 102-3. Cells 102-106 and their associated sectors are
geographically joined together to enable user terminals (UTs) 114
(e.g., mobile phones, laptops, tablets, pagers, or any other device
with an appropriate wireless modem) to wirelessly communicate over
a wide area with a core network 116 via BSs 108-112. Cellular
network 100 can be operated in accordance with any one of a number
of different cellular network standards, including one of the
current or yet to be released versions of the long-term evolution
(LTE) standard and the worldwide interoperability for microwave
access (WiMAX) standard.
[0022] For at least sector 102-1, BS 108 has an excess number of
transmit antennas available to transmit independent data streams
over the same time-frequency interval to two or more UTs 114
located in sector 102-1. BS 108 is configured to use the excess
transmit antennas in conjunction with precoding to appropriately
shape the independent data streams before they are transmitted to
reduce interference between the independent data streams or what is
referred to as inter-user interference. The excess transmit
antennas are specifically used to further focus the energy of each
independent data stream into narrower regions of space in
accordance with the concept of massive MIMO.
[0023] Referring now to FIG. 2, an exemplary block diagram of BS
108 is illustrated in accordance with embodiments of the present
disclosure. BS 108 includes, for transmitting downlink to UTs
located in sector 102-1, N transmit antennas 202-1 through 202-N, a
precoder 204, a data source 206, and a scheduler 208.
[0024] As explained above in FIG. 1, BS 108 is configured to
transmit independent data streams over the same time-frequency
interval to two or more UTs 114 located in sector 102-1. BS 108
uses precoder 204 to precode the independent data streams before
they are transmitted to reduce inter-user interference. Several
different precoding techniques can be used, including
matched-filter (MF) precoding, zero-forcing (ZF) precoding,
minimum-mean square error (MMSE) precoding, and, with some
modifications to precoder 204, non-linear precoding techniques such
as vector perturbation. In FIG. 2, the independent data streams are
specifically labeled s.sub.1 through S.sub.K and are provided to
precoder 204 by data source 206.
[0025] The precoded signal output by precoder 204 can be written
as:
x=.SIGMA..sub.i=1 to KF.sub.is.sub.i, (1)
where s.sub.i is the independent data stream for the i-th UT,
F.sub.i is an Nx1 precoding vector for the i-th UT, and K is the
number of independent data streams to be transmitted. Based on the
precoded signal x being appropriately fed to and transmitted by the
N transmit antennas 202-1 through 202-N, the symbol received by the
UT intended to receive the k-th independent data stream s.sub.k can
be written as:
y k = H k x + n k = H k i = 1 to K F i s i + n k , ( 2 )
##EQU00001##
where n.sub.k is a vector representing noise and H.sub.k is a 1xN
channel matrix for the UT.
[0026] The symbol y.sub.k includes interference from the symbols of
the independent data streams intended for other UTs. This component
of interference, as explained above, is referred to as inter-user
interference and can be written as:
H.sub.k.SIGMA..sub.i=1 to K.sup.i.noteq.kF.sub.is.sub.i . (3)
[0027] As noted above, BS 108 includes an excess number of transmit
antennas over the number of independent data streams S.sub.1
through S.sub.K to be transmitted. BS 108 is configured to use the
excess transmit antennas in conjunction with precoding to
appropriately shape the different independent data streams before
they are transmitted to reduce inter-user interference as given by
Eq. (3). The excess transmit antennas are specifically used to
further focus the energy of each independent data stream into
narrower regions of space in accordance with the concept of massive
MIMO.
[0028] Although inter-user interference can be reduced using the
concept of massive MIMO, for a practical number of excess transmit
antennas at BS 108, inter-user interference can still significantly
affect downlink data transmissions without proper scheduling.
Example scenarios where proper scheduling can better leverage the
narrower downlink beams to reduce inter-user interference are
described below.
[0029] Referring now to FIG. 3A, a scenario is shown using
exemplary cellular network 100 described above in FIG. 1 where
scheduling can be used to better leverage the narrower downlink
beams provided by massive MIMO to reduce inter-user interference
experienced by the at least three UTs 114-1, 114-2, and 114-3
located in and served by sector 102-1.
[0030] As shown in FIG. 3A, UT 114-1 is located in close proximity
to UT 114-3. Because UT 114-1 is located in close proximity to UT
114-3, downlink transmissions to UT 114-1 are more likely to
overlap and interfere with downlink transmissions to UT 114-3 that
occur over the same time-frequency interval. Depending on how close
UT 114-1 is to UT 114-3, the downlink transmissions to these two
UTs may overlap and interfere even with the narrower downlink beams
provided by the excess transmit antennas at BS 108.
[0031] Therefore, in one embodiment, scheduler 208, further
included in BS 108 as shown in FIG. 2, can select a sub-group of
UTs from among the UTs served by sector 102-1 to transmit
independent data streams to over the same time-frequency interval
based on the locations of the UTs. In particular, the sub-group of
UTs can be selected based on the locations of the UTs to limit
inter-user interference among the sub-group of UTs. For example,
scheduler 208 can include UTs in the sub-group of UTs that have
sufficient space between themselves and the other UTs included in
the sub-group of UTs. The amount of space deemed sufficient can be
determined based on, for example, the number of excess transmit
antennas available at BS 108 to transmit downlink to the UTs. This
is because more excess antennas support the formation of narrower
antenna beams. In the scenario shown in FIG. 3A, scheduler 208 may
select UT 114-2 and 114-3 to form, at least in part, one sub-group
of UTs and select UT 114-1 to form, at least in part, another
sub-group of UTs because of its close proximity to UT 114-3.
[0032] Scheduler 208 can receive the locations of the UTs served by
sector 102-1 as input as shown in FIG. 2. The locations of the UTs
served by sector 102-1 can be determined, for example, via
triangulation using the global positioning system (GPS) satellites
and/or via triangulation using BSs in cellular network 100.
[0033] In addition to the above, if two or more UTs served by
sector 102-1 receive downlink transmissions from BS 108 at similar
angles (relative to the orientation of the BS antennas), downlink
transmissions to the two or more UTs from BS 108 that occur over
the same time-frequency interval are more likely to overlap and
interfere.
[0034] Therefore, in another embodiment, scheduler 208 can select a
sub-group of UTs from among the UTs served by sector 102-1 to
transmit independent data streams to over the same time-frequency
interval based on the angle at which downlink signals from BS 108
are received by the UTs. In particular, the sub-group of UTs can be
selected based on the angle at which downlink signals from BS 108
are received by the UTs to limit inter-user interference among the
sub-group of UTs. For example, scheduler 208 can include UTs in the
sub-group of UTs that receive downlink signals from BS 108 at
sufficiently different angles than the other UTs included in the
sub-group of UTs.
[0035] Scheduler 208 can receive the angles at which downlink
signals from BS 108 are received by the UTs served by sector 102-1
as input as shown in FIG. 2. As would be appreciated by one of
ordinary skill in the art, the angle at which a downlink signal
transmitted by BS 108 is received by a UT can be determined, for
example, based on the angle at which an uplink signal transmitted
by the UT is received by BS 108, as these angles are likely
reciprocal.
[0036] After selecting a sub-group of UTs based on the location of
the UTs or the angle at which downlink signals from BS 108 are
received by the UTs, scheduler 208 can schedule an independent data
stream for each UT in the sub-group of UTs for downlink
transmission over the same time-frequency interval. As shown in
FIG. 2, scheduler 208 can specifically control data source 206 to
provide the independent data streams for each UT in the sub-group
of UTs at an appropriate time for precoding by precoder 204 and
downlink transmission by transmit antennas 202-1 through 202-N.
[0037] Referring now to FIG. 3B, another scenario is shown using
exemplary cellular network 100 described above in FIG. 1 where
scheduling can be used to better leverage the narrower downlink
beams provided by massive MIMO to reduce inter-user interference
experienced by an edge UT 114-4 served by sector 102-2 from
downlink transmissions to one or more of the at least three UTs
114-1. 114-2, and 114-3 served by sector 102-1. An edge UT, such as
edge UT 114-4, is a UT that is at or near the edge of a sector of a
cell.
[0038] Typically, UTs in one sector of a cell experience negligible
amounts of interference from the downlink transmissions to UTs in
another, adjacent sector of a cell. This is because the energies of
downlink transmissions emitted by the transmit antennas of one
sector are mainly contained within that sector and only low levels
of energy from those downlink transmissions permeate into adjacent
sectors. However, for an edge UT that is at or near the edge of the
sector it is served by, the downlink transmissions to UTs in the
sector adjacent to the sector serving the edge UT can interfere
with the edge UTs ability to receive downlink transmissions.
[0039] Therefore, coordination techniques were developed to prevent
the downlink transmissions from the adjacent sector from
interfering with the downlink transmissions to the edge UT from its
serving sector. For example, in one such coordination technique,
the BS of the adjacent sector is prevented from transmitting
downlink to the UTs of the adjacent sector over the same
time-frequency interval that the BS of the sector serving the edge
UT is transmitting downlink to the edge UT. In another coordination
technique, the BS of the adjacent sector transmits downlink over
the same time-frequency interval that the BS of the sector serving
the edge UT is transmitting downlink to the edge UT but with a
reduced power level to limit interference. In general, both
techniques require some coordination between the BSs of the two
cells or, if the two sectors are served by the same BS, some
coordination between the hardware used by the BS for each
sector.
[0040] With the narrower downlink beams provided by massive MIMO, a
different coordination technique involving scheduling can be
implemented to reduce inter-user interference (also referred to as
inter-sector interference in this context) experienced by the edge
UT 114-4 from downlink transmissions to one or more of the at least
three UTs 114-1, 114-2, and 114-3.
[0041] For example, as shown in FIG. 3B, UT 114-3 served by sector
102-1 is located in close proximity to UT 114-4 served by sector
102-2. Because UT 114-3 is located in close proximity to UT 114-4,
downlink transmissions to UT 114-3 are more likely to overlap and
interfere with downlink transmissions to UT 114-4 that occur over
the same time-frequency interval even with narrower downlink beams.
Downlink transmissions to the other UTs 114-1 and 114-2 are less
likely to overlap and interfere with downlink transmissions to UT
114-4 that occur over the same time-frequency interval because of
the distance between the UTs.
[0042] Therefore, in one embodiment, scheduler 208 can select a
sub-group of UTs from among the UTs served by sector 102-1 to
transmit independent data streams to over the same time-frequency
interval that edge UT 114-4 is scheduled to receive an independent
data stream based on the locations of the UTs. In particular, the
sub-group of UTs can be selected based on the locations of the UTs
served by sector 102-1 and the location of edge UT 114-4 to limit
inter-user interference at edge UT 114-4. For example, scheduler
208 can include UTs in the sub-group of UTs that have sufficient
space between themselves and the edge UT 114-4. The amount of space
deemed sufficient can be determined based on, for example, the
number of excess transmit antennas available at BS 108 to transmit
downlink to the UTs served by sector 102-1.
[0043] In the scenario shown in FIG. 3B, scheduler 208 may select
UT 114-1 and 114-2 to form one sub-group of UTs and schedule
independent data streams for transmission to those UTs over the
same time-frequency interval that edge UT 114-4 is scheduled to
receive an independent data stream. Because of its close proximity
to UT 114-4, scheduler 208 may further select UT 114-3 to form, at
least in part, another sub-group of UTs and schedule independent
data streams for transmission to those UTs over a different
time-frequency interval than edge UT 114-4 is scheduled to receive
an independent data stream to limit inter-user interference (or
inter-sector interference) at edge UT 114-4.
[0044] Scheduler 208 can receive the locations of the UTs served by
sector 102-1 and the location of edge UT 114-4 as input. The
location of edge UT 114-4 can be sent to scheduler 208 via a
message from the hardware used by BS 108 to communicate with the
UTs of sector 102-2. In addition to the location of edge UT 114-4,
messages can be passed between the respective hardware used by BS
108 to communicate with the UTs of sectors 102-1 and 102-2 to
determine a time and/or frequency that downlink transmissions are
scheduled to be transmitted to edge UT 114-4. This message passing
between the respective hardware used by BS 108 to communicate with
the UTs of sectors 102-1 and 102-2 can viewed as a type of
coordination between sectors 102-1 and 102-2.
[0045] It should be noted that edge UT 114-4 can be located on the
edge of a sector of a different cell than cell 102. For example, as
shown in FIG. 3C, edge UT 114-4 can be served by and located on the
edge of a sector in cell 106. The same scheduling technique
described above can be used to reduce inter-user interference (or
inter-cell interference in this context) experienced by edge UT
114-4 from downlink transmissions to one or more of the at least
three UTs 114-1, 114-2, and 114-3. The main difference would be
that the messages described above would be passed between BS 108
and BS 112.
[0046] Referring now to FIG. 3D, a scenario is shown again using
exemplary cellular network 100 described above in FIG. 1 where
scheduling can be used to better leverage the narrower downlink
beams provided by massive MIMO to reduce inter-user interference
experienced by the at least three UTs 114-1, 114-2, and 114-3
located in and served by sector 102-1 of cell 102.
[0047] In general, as opposed to just selecting a sub-group of UTs
from among the UTs served by sector 102-1 to transmit independent
data streams to over the same time-frequency interval based on the
locations of the UTs, as described above in FIG. 3A, FIG. 3D
illustrates that selecting the sub-group of UTs based on locations
of the UTs and the direction of movement of the UTs can be further
beneficial. In particular, the direction of movement of the UTs can
be used to predicate whether two UTs will eventually come in close
proximity to each other such that the two UTs should not be
selected to be a part of a sub-group of UTs to schedule independent
data streams for transmission to over the same time-frequency
interval. Assuming two UTs eventually come in close proximity to
each other, the downlink transmissions to the two UTs may overlap
and interfere even with the narrower downlink beams provided by the
excess transmit antennas at BS 108.
[0048] For example, FIG. 3D illustrates the location of UTs 114-1,
114-2, and 114-3 and further illustrates a vector 118 that shows
the direction of movement of UT 114-3. Scheduler 208 can select a
sub-group of UTs from among the UTs served by sector 102-1 to
transmit independent data streams to over the same time-frequency
interval based on the locations of the UTs and the direction of
movement of UT 114-3. In particular, the sub-group of UTs can be
selected based on the locations of the UTs and the direction of
movement of UT 114-3 to limit inter-user interference among the
sub-group of UTs. For example, scheduler 208 can include UTs in the
sub-group of UTs that have sufficient space between themselves and
the other UTs included in the sub-group of UTs and that are
predicted, based on their current direction of movement, to not
come in close proximity to one another. In the scenario shown in
FIG. 3D, scheduler 208 may select UT 114-2 and 114-3 to form, at
least in part, one sub-group of UTs but not include UT 114-1 in
such a group because, based on the location of 114-3 and its
current direction of movement, it may come within close proximity
to UT 114-1.
[0049] In another embodiment, the number of UTs in a sub-group to
receive independent data streams over the same time-frequency
interval can be adjusted or determined based on a speed of one or
more UTs in the sub-group. If one or more UTs in the sub-group are
moving fast, as determined for example based on some speed
threshold, then the number of UTs in the sub-group can be reduced.
If, on the other hand, one or more UTs in the sub-group are moving
slow, as determined for example based on some speed threshold, then
the number of UTs in the sub-group can be increased.
[0050] The average speed of one or more UTs in the sub-group can
also be used to determine or adjust the number of UTs in the
sub-group that are to receive independent data streams over the
same time-frequency interval. For example, if the average speed is
fast, as determined for example based on some speed threshold, then
the number of UTs in the sub-group can be reduced. If, on the other
hand, the average speed is slow, as determined for example based on
some speed threshold, then the number of UTs in the sub-group can
be increased.
[0051] Finally, if the speed of a UT in the sub-group is above some
speed threshold, that UT can be removed from the sub-group and
transmitted to downlink in an SU-MIMO mode to reduce inter-user
interference. Scheduler 208 can further perform the above noted
adjustments based on speed.
[0052] In another embodiment, the beam widths associated with the
downlink transmissions to one or more of the UTs served by sector
102-1 can be adjusted. For example, the beam width of a downlink
transmission to a UT served by sector 102-1 can be adjusted based
on a speed at which the UT is moving. If the UT is moving fast, it
may be hard to continually update the direction of the beam of
downlink transmission at the UT. Therefore, the beam width of the
downlink transmission can be widened so that the UT has a wider
area over which to receive the downlink transmission.
[0053] In another embodiment. the beam widths associated with the
downlink transmissions to one or more of the UTs served by sector
102-1 can be adjusted based on a desired downlink throughput and/or
desired reliability with which the downlink data is received by the
UT. In general, widening the beam width may reduce the overall
energy density of the beam and downlink data rate to the UT, but
may improve the reliability with which the downlink data is
received by the UT, and narrowing the beam width may increase the
overall energy density of the beam and downlink data rate to the
UT, but may reduce the reliability with which the downlink data is
received by the UT.
[0054] In one embodiment, the beam width of a downlink transmission
to a
[0055] UT is adjusted by adjusting the precoding vector used to
precode the downlink transmission to the UT. In another embodiment,
the beam width is adjusted by increasing or reducing the number of
excess transmit antennas at BS 108 used to transmit downlink to the
UT.
[0056] Referring now to FIG. 4, a flowchart 400 of a method for
scheduling in a cellular communication system that uses a large
number of excess transmit antennas is illustrated in accordance
with embodiments of the present disclosure. The method of flowchart
400 can be implemented by BS 108 as described above and illustrated
in FIG. 2. However, it should be noted that the method can be
implemented by other systems and components as well.
[0057] The method of flowchart 400 begins at step 402. At step 402,
a sub-group of UTs from among a group of UTs served a first sector
of a cellular network, such as sector 102-1 illustrated in FIG. 1,
is selected to limit inter-user interference. More specifically, as
discussed above, the sub-group of UTs is selected to limit
inter-user interference among the sub-group of UTs and/or to limit
inter-user interference experienced by a UT that is at or near the
boundary of a sector that is adjacent to the sector that serves the
sub-group of UTs. For example, as discussed above, the sub-group of
UTs can be selected to serve one of these purposes based on a
location of one or more UTs, an angle of arrival of downlink
transmissions at one or more UTs, or a location and direction of
movement of one or more UTs. After the sub-group of UTs is
selected, flowchart 400 proceeds to step 404.
[0058] At step 404, a different data stream for transmission over a
same time-frequency interview is scheduled for each UT in the
sub-group.
[0059] Finally, at step 406, the different data streams are
precoded to produce precoded data streams for transmission over the
same time-frequency interval by more antennas than the number of
precoded data streams.
[0060] It should be noted that, although the present disclosure was
described above as being directed to a system and method for
selecting a sub-group of UTs to schedule independent downlink data
streams for transmission to over the same time-frequency interval,
it will be apparent to one of ordinary skill in the art based on
the teachings herein that the same system and method with slight
modifications can be used for selecting a sub-group UTs to schedule
independent uplink data streams for transmission to over the same
time-frequency interval.
III. Example Computer System Environment
[0061] It will be apparent to persons skilled in the relevant
art(s) that various elements and features of the present
disclosure, as described herein, can be implemented in hardware
using analog and/or digital circuits, in software, through the
execution of instructions by one or more general purpose or
special-purpose processors, or as a combination of hardware and
software.
[0062] The following description of a general purpose computer
system is provided for the sake of completeness. Embodiments of the
present disclosure can be implemented in hardware, or as a
combination of software and hardware. Consequently, embodiments of
the disclosure may be implemented in the environment of a computer
system or other processing system. An example of such a computer
system 500 is shown in FIG. 5. Modules depicted in FIGS. 1 and 2
may execute on one or more computer systems 500. Furthermore, each
of the steps of the flowchart depicted in FIG. 4 can be implemented
on one or more computer systems 500.
[0063] Computer system 500 includes one or more processors, such as
processor 504. Processor 504 can be a special purpose or a general
purpose digital signal processor. Processor 504 is connected to a
communication infrastructure 502 (for example, a bus or network).
Various software implementations are described in terms of this
exemplary computer system. After reading this description, it will
become apparent to a person skilled in the relevant art(s) how to
implement the disclosure using other computer systems and/or
computer architectures.
[0064] Computer system 500 also includes a main memory 506,
preferably random access memory (RAM), and may also include a
secondary memory 508. Secondary memory 508 may include, for
example, a hard disk drive 510 and/or a removable storage drive
512, representing a floppy disk drive, a magnetic tape drive, an
optical disk drive, or the like. Removable storage drive 512 reads
from and/or writes to a removable storage unit 516 in a well-known
manner. Removable storage unit 516 represents a floppy disk,
magnetic tape, optical disk, or the like, which is read by and
written to by removable storage drive 512. As will be appreciated
by persons skilled in the relevant art(s), removable storage unit
516 includes a computer usable storage medium having stored therein
computer software and/or data.
[0065] In alternative implementations, secondary memory 508 may
include other similar means for allowing computer programs or other
instructions to be loaded into computer system 500. Such means may
include, for example, a removable storage unit 518 and an interface
514. Examples of such means may include a program cartridge and
cartridge interface (such as that found in video game devices), a
removable memory chip (such as an EPROM, or PROM) and associated
socket, a thumb drive and USB port, and other removable storage
units 518 and interfaces 514 which allow software and data to be
transferred from removable storage unit 518 to computer system
500.
[0066] Computer system 500 may also include a communications
interface 520. Communications interface 520 allows software and
data to be transferred between computer system 500 and external
devices. Examples of communications interface 520 may include a
modem, a network interface (such as an Ethernet card), a
communications port, a PCMCIA slot and card, etc. Software and data
transferred via communications interface 520 are in the form of
signals which may be electronic, electromagnetic, optical, or other
signals capable of being received by communications interface 520.
These signals are provided to communications interface 520 via a
communications path 522. Communications path 522 carries signals
and may be implemented using wire or cable, fiber optics, a phone
line, a cellular phone link, an RF link and other communications
channels.
[0067] As used herein, the terms "computer program medium" and
"computer readable medium" are used to generally refer to tangible
storage media such as removable storage units 516 and 518 or a hard
disk installed in hard disk drive 510. These computer program
products are means for providing software to computer system
500.
[0068] Computer programs (also called computer control logic) are
stored in main memory 506 and/or secondary memory 508. Computer
programs may also be received via communications interface 520.
Such computer programs, when executed, enable the computer system
500 to implement the present disclosure as discussed herein. In
particular, the computer programs, when executed, enable processor
504 to implement the processes of the present disclosure, such as
any of the methods described herein. Accordingly, such computer
programs represent controllers of the computer system 500. Where
the disclosure is implemented using software, the software may be
stored in a computer program product and loaded into computer
system 500 using removable storage drive 512, interface 514, or
communications interface 520.
[0069] In another embodiment, features of the disclosure are
implemented primarily in hardware using, for example, hardware
components such as application-specific integrated circuits (ASICs)
and gate arrays. Implementation of a hardware state machine so as
to perform the functions described herein will also be apparent to
persons skilled in the relevant art(s).
IV. Conclusion
[0070] Embodiments have been described above with the aid of
functional building blocks illustrating the implementation of
specified functions and relationships thereof. The boundaries of
these functional building blocks have been arbitrarily defined
herein for the convenience of the description. Alternate boundaries
can be defined so long as the specified functions and relationships
thereof are appropriately performed.
[0071] The foregoing description of the specific embodiments will
so fully reveal the general nature of the disclosure that others
can, by applying knowledge within the skill of the art, readily
modify and/or adapt for various applications such specific
embodiments, without undue experimentation, without departing from
the general concept of the present disclosure. Therefore, such
adaptations and modifications are intended to be within the meaning
and range of equivalents of the disclosed embodiments, based on the
teaching and guidance presented herein. it is to be understood that
the phraseology or terminology herein is for the purpose of
description and not of limitation, such that the terminology or
phraseology of the present specification is to be interpreted by
the skilled artisan in light of the teachings and guidance.
* * * * *