U.S. patent application number 13/545361 was filed with the patent office on 2012-11-01 for intelligent mode switching in communication networks.
This patent application is currently assigned to Adaptix, Inc.. Invention is credited to Xun Shao, Manyuan Shen, Guanbin Xing.
Application Number | 20120275387 13/545361 |
Document ID | / |
Family ID | 46513080 |
Filed Date | 2012-11-01 |
United States Patent
Application |
20120275387 |
Kind Code |
A1 |
Xing; Guanbin ; et
al. |
November 1, 2012 |
Intelligent Mode Switching In Communication Networks
Abstract
Systems and methods for intelligently switching between
communication modes. An optimum communication mode is selected
based upon determining the mobility of the subscriber station, the
location of the subscriber station, and orthogonality of signals
received from the subscriber station with respect to a signal of
another subscriber station. Each determination may be continually
or incrementally performed according to the passage of a time
interval or upon observation of changes in relevant conditions.
Inventors: |
Xing; Guanbin; (Issaquah,
WA) ; Shen; Manyuan; (Bellevue, WA) ; Shao;
Xun; (Bellevue, WA) |
Assignee: |
Adaptix, Inc.
Bellevue
WA
|
Family ID: |
46513080 |
Appl. No.: |
13/545361 |
Filed: |
July 10, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11963265 |
Dec 21, 2007 |
8228809 |
|
|
13545361 |
|
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Current U.S.
Class: |
370/328 |
Current CPC
Class: |
H04B 7/0669 20130101;
H04B 7/0857 20130101; H04W 72/046 20130101; H04L 1/0006 20130101;
H04B 7/0689 20130101; H04B 7/0617 20130101; H04B 7/0413 20130101;
H04L 1/0015 20130101; H04L 1/0643 20130101 |
Class at
Publication: |
370/328 |
International
Class: |
H04W 8/02 20090101
H04W008/02 |
Claims
1. A base station comprising: one or more processors determining
the mobility of a subscriber station, determining the position of
said subscriber station, and determining either spatial
orthogonality of the signal of said subscriber station with respect
to at least another subscriber station signal or whether a Line of
Sight (LOS) condition is associated with said subscriber station,
wherein at least one of said one or more processors determines
whether said subscriber station is static or dynamic and determines
whether said subscriber station is closer to a cell boundary or
closer to said base station; and an antenna communication scheme
based upon said determined mobility, said determined position, and
one of said determination of said spatial orthogonality of the
signal and said determination of said LOS condition.
2. The base station of claim 1, wherein said at least one of said
one or more processors determines whether said subscriber station
is a member of a pair of orthogonal subscriber stations.
3. The base station of claim 1, wherein said at least one of said
one or more processors determines whether more than one antenna is
associated with said subscriber station.
4. The base station of claim 1, further comprising: logic for
selecting Multiple-Input Multiple-Output (MIMO) for a communication
mode if said LOS condition is determined not to be associated with
said subscriber station.
5. The base station of claim 1, further comprising: logic for
selecting Space Division Multiple Access (SDMA) for a communication
mode if said LOS condition is determined to be associated with said
subscriber station.
6. The base station of claim 1, further comprising: logic to select
Maximum Ratio Combining (MRC) for a communication mode if said
subscriber station is determined to be dynamic.
7. The base station of claim 1, further comprising: logic to select
Space Time Block Code (STBC) for a communication mode if said
subscriber station is determined to be dynamic.
8. The base station of claim 1, further comprising: logic to select
Multiple-Input Multiple-Output (MIMO) for a communication mode if
said subscriber station is determined to be dynamic.
9. The base station of claim 1, further comprising: logic to select
Maximum Ratio Combining (MRC) for a communication mode if said
subscriber station is determined to be closer to said cell
boundary.
10. The base station of claim 1, further comprising: logic to
select Beam Forming (BF) for a communication mode if said
subscriber station is determined to be closer to said cell
boundary.
11. A system including a subscriber station, said system
comprising: one or more processors determining the mobility of said
subscriber station, determining the position of said subscriber
station, and determining either spatial orthogonality of the signal
of said subscriber station with respect to at least another
subscriber station signal or whether a Line of Sight (LOS)
condition is associated with said subscriber station and selecting
a multiple antenna communication is further based upon one of said
determination of said spatial orthogonality of the signal and said
determination of said LOS condition, wherein at least one of said
one or more processors determines whether said subscriber station
is static or dynamic and determines whether said subscriber station
is closer to a cell boundary or closer to said subscriber
station.
12. The system of claim 11, wherein said at least one of said one
or more processors determines whether said subscriber station is a
member of a pair of orthogonal subscriber stations.
13. The system of claim 11, wherein said at least one of said one
or more processors determines whether more than one antenna is
associated with said subscriber station.
14. The system of claim 11, further comprising: logic for selecting
Multiple-Input Multiple-Output (MIMO) for a communication mode if
said LOS condition is determined not to be associated with said
subscriber station.
15. The system of claim 11, further comprising: logic for selecting
Space Division Multiple Access (SDMA) for a communication mode if
said LOS condition is determined to be associated with said
subscriber station.
16. The system of claim 11, further comprising: logic to select
Maximum Ratio Combining (MRC) for a communication mode if said
subscriber station is determined to be dynamic.
17. The system of claim 11, further comprising: logic to select
Space Time Block Code (STBC) for a communication mode if said
subscriber station is determined to be dynamic.
18. The system of claim 11, further comprising: logic to select
Multiple-Input Multiple-Output (MIMO) for a communication mode if
said subscriber station is determined to be dynamic.
19. The system of claim 11, further comprising: logic to select
Maximum Ratio Combining (MRC) for a communication mode if said
subscriber station is determined to be closer to said cell
boundary.
20. The system of claim 11, further comprising: logic to select
Beam Forming (BF) for a communication mode if said subscriber
station is determined to be closer to said cell boundary.
Description
[0001] This application is a continuation of U.S. application Ser.
No. 11/963,265, filed Dec. 21, 2007; which is incorporated by
reference herein.
TECHNICAL FIELD
[0002] The present invention generally relates to communication
networks. In particular, the present invention relates to systems
and methods for providing intelligent communication mode switching
in the uplink and/or downlink for communication across a
network.
BACKGROUND OF THE INVENTION
[0003] In communication networks, different schemes have been used
to improve communication between a base station (BS) and subscriber
station (SS) across the network. For example, some networks employ
a single transmit antenna and single receive antenna at the BS and
subscriber station SS. These systems may improve communication,
i.e., increase SINR, by employing adaptive coding/modulation
schemes, where the signal modulation scheme is adjusted to
effectuate an increase in SINR. Other networks employ different
antenna array modes, i.e., modes of communication, between a BS and
a SS where each of the BS and SS have multiple antennas. Examples
of these multiple antenna array communication modes include
Space-Time Block Code (STBC), Multiple-Input Multiple-Output
(MIMO), Space Division Multiple Access (SDMA), and beam forming
(BF) techniques. Each of these multiple antenna array communication
modes is advantageously used under certain conditions, but are of
only limited usefulness under other conditions. For example, SDMA
schemes provide good coverage and efficient use of available
spectrum, but are limited to effective use only with non-moving or
slow-moving SSs. An STBC scheme is best used for fast-moving,
dynamic SSs, but provides less efficient use of available spectrum.
On the other hand, a Beam Forming (BF) scheme is most effective for
communications involving subscribers at or near cell boundaries as
it can be used to increase signal strength and reduce interference
from other cells.
[0004] More often than not, simply employing a single mode of
communication for communication is not practical because any given
mode is not versatile enough to be useful across a sufficiently
wide range of conditions. As such, schemes have been employed where
the network switches from one mode of communication to another to
accommodate the changing conditions. Nevertheless, these schemes
are somewhat limited in that they only provide switching between,
at best, two modes. Also, such systems are limited because they
typically consider only SS position when deciding to switch between
communication modes. While some of these systems are touted as
being operable to switch between multiple antenna modes; at best,
these systems switch between only two modes and are limited to
point-to-point communication. Further, these systems do not
optimize communication mode selection point-to-multiple-point in a
multi-cell context.
[0005] By way of example, suppose a user is operating in a LAN type
environment. In all likelihood, the user will have only one
available communication scheme, e.g., MIMO, across the network.
Another communication mode, e.g., BF will not be available to that
user because it has not been implemented in such an environment. Of
course, BF has been implemented in such networks, typically in a
proprietary form in the CDMA context, and the like. However, in no
case has MIMO, for example, been additionally implemented in the
same network. Accordingly, a user of the network has been forced to
settle for one mode of communication or another.
SUMMARY OF THE INVENTION
[0006] In view of the above, there is a need for an intelligent
method of switching between various modes of communication in a
communication network. Such an intelligent system should be able to
be employed in a wide-range of networks including, for example LAN
and WiMAX. Further, such an intelligent method would be based upon,
for example, the number of antennas associated with a SS and
communication channel conditions. The ultimate goal of such an
intelligent method is to insure link reliability and maximize
overall system capacity while having an intelligent algorithm that
facilitates on-the-go switching between modes of communication on a
per user basis.
[0007] A preferred embodiment of the present invention provides
systems and methods for selecting modes of communication over a
network. According to such systems and methods, an algorithm
involves determining the mobility of said subscriber station,
determining the position of said subscriber station, and
determining orthogonality of the signal of said subscriber station
with respect to another subscriber. Based upon these
determinations, a communication mode maybe selected to optimize
link reliability and/or optimize network performance.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] For a more complete understanding of the present invention,
reference is now made to the following descriptions taken in
conjunction with the accompanying drawing, in which:
[0009] FIG. 1 is a system according to a preferred embodiment of
the present invention;
[0010] FIG. 2 is a flow diagram for determining a communication
mode in the uplink according to a preferred embodiment of the
present invention;
[0011] FIG. 3 is a flow diagram for determining a communication
mode in the uplink according to another embodiment of the present
invention;
[0012] FIG. 4 is a flow diagram for determining a communication
mode in the downlink according to a preferred embodiment of the
present invention; and
[0013] FIG. 5 is a flow diagram for determining a communication
mode in the downlink according to another embodiment of the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0014] Referring to FIG. 1, communication system 100 is adapted to
provide intelligent communication mode switching in the uplink
(communications from the SS to the BS) and the downlink
(communications from the BS to SS). System 100 can be generalized
to most communication networks and includes network components as
known in the art adapted to provide operation as described herein.
BS 101 communicates with SS 102-1 through 102-N and vice versa in
cell A, BS 103 communicates with SSs 104-1 though 104-N and vice
versa in cell B, and BS 105 communicates with SSs 106-1 through
106-N and vice versa in cell C. Each of BS 101, 103, and 105
communicate on "backhaul" network 107 via communication means 108.
Communication means 108 may comprise phone lines, RF communication
components, and the like as known in the art.
[0015] As will be described in greater detail below, system 100
implements an intelligent methodology whereby an iterative process
is executed to select, from a number of possibilities, which mode
of communication to use between a BS and SS. System 100 and its
related methodology applies a detailed mode switching algorithm not
known in the art. According to preferred embodiments, the algorithm
is used to select an optimum mode of communication based upon a
sequence of determinations, including 1) SS mobility (i.e., a
static or dynamic MS); 2) SS distance (i.e., relative distance
between the SS and the BS and cell); and 3) SS orthogonality (i.e.,
whether the SS part of an orthogonal pair of SSs). Preferably, the
algorithm executes these determination in the order provided above
to make for an efficient and exceptionally robust scheme of
communication mode switching. Advantageously, the methodology can
be employed while the BS is communicating with a SS. Accordingly,
the communication mode can be changed from one to another to ensure
that the communication is optimized as conditions change during the
call. It naturally follows that the methodology can be changed
employed during handoff operations.
[0016] The present invention also relates to apparatus, e.g., BSs
and SSs, for performing the operations herein. A BS or SS may be
specially constructed for the required purposes, or it may comprise
a general-purpose processor, selectively activated or configured by
a program stored in the processor. Such a r program may be stored
in a computer readable storage medium, such as, optical disks,
CD-ROMs, and magnetic-optical disks, read-only memories (ROMs),
random access memories (RAMs), EPROMs, EEPROMs, magnetic or optical
cards, or any type of media suitable for storing electronic
instructions, and each coupled to a computer system bus. The
algorithms and displays presented herein are not inherently related
to any particular computer or other apparatus. Various general
purpose systems may be used with programs in accordance with the
teachings herein, or it may prove convenient to construct more
specialized apparatus to perform the required method steps. The
required structure for a variety of these systems will appear from
the description below. In addition, the present invention is not
described with reference to any particular programming language. It
will be appreciated that a variety of programming languages may be
used to implement the teachings of the invention as described
herein. A machine-readable medium includes any mechanism for
storing or transmitting information in a form readable by a machine
(e.g., a computer). For example, a machine-readable medium includes
read only memory ("ROM"); random access memory ("RAM"); magnetic
disk storage media; optical storage media; flash memory devices;
electrical, optical, acoustical or other form of propagated
signals, e.g., carrier waves, infrared signals, digital signals,
etc.
[0017] System 100 can be implemented in a number of communication
networks such as, for example, a WiMAX communication network, i.e.,
a system based on the IEEE 802.16 standard. By way of such an
example, suppose system 100 is implemented in a WiMAX communication
network. Accordingly, system 100 would be capable of supporting
modes of communication to a user as set forth in the WiMAX
standard. That is, in the uplink a SS user could employ, for
example, Maximum Ratio Combining (MRC), SDMA, MIMO, or circular
delay diversity (CDD). In the downlink, there would be even more
available modes of communication. Available communication mode
choices include STBC, MIMO, SDMA, beam forming, and the like.
[0018] Referring to FIG. 2, a general overview of a preferred
intelligent methodology of selectively choosing a mode of uplink
communication according to system 100 is shown as method 200.
Specific implementations will be described thereafter. Method 200
employs the intelligent algorithm described above to select the
optimum mode of communication between a BS and SS. Accordingly, as
will be further described, method 200 generally involves
determining SS mobility, SS distance, and SS signal orthogonality
with respect to at least one other SS. In this context, SSs are
considered to be orthogonal to one another where their signals are
such that cross-talk (e.g., co-channel interference, and is related
to adjacent-channel interference) between their signals are
significantly reduced or eliminated.
[0019] According to FIG. 2, at 201, a BS, such as for example BS
101 shown in FIG. 1, determines what modes are available for
communication with a number of SSs, such as for example SS 102-1
through 102-N as shown in FIG. 1. BS 101 makes this determination
based, in part, on information received from SSs within its cell,
relating to the capabilities of those SSs. Also, BS 101 makes this
determination in view of the specific communication standard or
protocol that has been specified. For example, the WLAN standard
does not allow SDMA or BF modes, whereas WiMAX specified these
modes and others. It should be appreciated that, according to
particular embodiments, each of SS 102-1 through 102N may solely or
partially determine which modes of communication are selected. In
such embodiments, each SS 102 may be equipped with software and/or
hardware capable of utilizing information necessary to select which
modes of communication are used, or relay pertinent information to
a BS, where the BS utilizes the information received from each SS
to make the selection itself. As will be described in further,
these concepts apply equally to uplink and downlink
communications.
[0020] At 202, BS 101 determines the number of antennas for use in
the transmission and/or reception associated with the SS. Such
information may be provided to BS 101 by each SS 102. Based on that
determination, BS 101 eliminates one or more otherwise available
modes of communication for communication with that SS.
Specifically, BS 101 eliminates from selection those modes for a
particular link direction (e.g., uplink and/or downlink) best
suited for SSs having multiple antennas where a SS has been
determined to have a singe antenna available for use with respect
to that link direction, and vice versa.
[0021] At 203, BS 101 determines if the SS is non-moving or
slow-moving, or fast-moving. According to a preferred embodiment,
what constitutes fast-moving will depend on system settings and can
be thought of in terms of a threshold set at BS 101. Based on that
determination, BS 101 may eliminate one or more otherwise available
modes of communication from selection.
[0022] At 204, BS 101 determines the relative position of the SS
within the cell. That is, BS 101 determines whether the SS is
closer to the cell boundary or closer to BS 101. Based on that
determination, BS 101 may eliminate one or more otherwise available
modes of communication from selection.
[0023] At 205, BS 101 determines orthogonality of the SS signal
with respect to at lease on other SS signal. According to
particular embodiments, such a determination may involve
determining if the SS is part of an orthogonal pair of SSs. Based
on that determination, BS 101 may eliminate one or more otherwise
available modes of communication from selection. Taken together,
the determinations described above narrow down the filed of modes
available for selection.
[0024] At 206, once the intelligent methodology described above is
executed, there may be no more than one of the originally available
modes left for selection. However, in the event more than one of
the original modes of communication remains for selection, BS 101
may select a single mode based on a number of criteria such as, for
example link reliability or implementation complexity. Also, each
mode may be prioritized according to one or more metrics, such that
BS 101 selects from the group of available modes according to the
priority of the available modes.
[0025] At 207, BS 101 reevaluates the mode of communication being
used to determine if that mode is still the optimal mode. This
reevaluation may be prompted by the passage of a predetermined time
interval as previously determined by BS 101, or may be prompted by
observation of one or more changes in relevant conditions. The
reevaluation process may prompt method 200 to begin at one of the
steps described above, such that the entire method 200 need not
necessarily be repeated.
[0026] Referring to FIG. 3, a specific implementation of method 200
is shown. In FIG. 3, generalized method 200 is implemented more
specifically as method 300 in a communication network operating
according to the WiMAX standard. The present inventors have found
that, in a WiMAX network, uplink SDMA communication is generally
desirable only for static or slow-moving SSs that are relatively
close to the BS, and provide high spectrum efficiency (e.g.,
greater than four bits/sec./Hz.). Accordingly, highly mobile users
are first eliminated from uplink SDMA communication. The
determination of a fast-moving SS is based upon, for example,
channel variance measurements performed at the BS over time. Also,
based on RSSI/CINR measurements performed at the BS, the position
of the SS within the cell is determined, i.e., SS location with
respect to the BS and cell boundary. If the SS is determined to be
relatively close to the cell boundary, that SS is eliminated from
SDMA uplink communication. Further, orthogonally among SSs is
critical to achieving expected gain. Therefore, only orthogonal SSs
are assigned as SDMA pairs for uplink communication. The
orthogonality of a pair SSs may be determined using uplink sounding
techniques.
[0027] In furtherance of the above, at 301, a BS determines what
modes are available for communication with a number of SSs. The BS
makes this determination based, in part, on information relating to
the capability of the SS with which it is communicating. For
instance, each SS may inform the BS of its capabilities via SBC
messages that include information relating to the number of
transmit/receive antennas and/or modes of communication supported
by each SS. At 302, the BS determines the number of transmit and/or
receive antennas associated with the MS; this determination may be
based upon, for example, SBC messages received from the SS. If the
SS has one transmit antenna, the BS proceeds along the single
antenna decision-making process. At 303, the BS determines if the
SS is a fast-moving base station. As mentioned, this determination
may be based upon channel variance measurements over time. If the
BS determines the SS is fast-moving, the BS selects the MRC mode of
communication for uplink communication with that SS. If not, the BS
proceeds with the decision-making process. At 304, the BS
determines the relative position of the SS within the cell. As
mentioned, this determination may be based upon RSSI/CINR
measurements performed at the BS. If the BS determines the SS is
closer to the cell boundary than the BS, the BS selects the MRC
mode of communication for uplink communication with that SS. If
not, the BS proceeds with the decision-making process. At 305, the
BS determines if the SS is part of an orthogonal pair of SSs. If
not, the BS selects the MRC mode of communication for communication
with that SS on the uplink. If the SS is part of an orthogonal
pair, the BS selects SDMA communication mode for communication on
the uplink. As mentioned, orthogonality may be determined by uplink
sounding techniques.
[0028] If, at 302, the BS determines the SS has more than one
transmit/receive antenna, the BS proceeds along the multiple
antenna decision-making process of FIG. 3. In the event the SS has
more than one antenna, it is possible to overlay a Circular Delay
Diversity (CDD) scheme on top of the MRC scheme at the transmitter
side. At 306, the BS determines if the SS is a fast-moving base
station. As mentioned, this determination may be based upon channel
variance measurements over time. If the BS determines the SS is
fast-moving, the BS selects TX: CDD and RX: MRC mode of
communication for uplink communication with that SS. If not, the BS
proceeds with the decision-making process. At 307, the BS
determines the relative position of the SS within the cell. As
mentioned, this determination may be based upon RSSI/CINR
measurements performed at the BS. If the BS determines the SS is
closer to the cell boundary than the BS, the BS selects TX: CDD and
RX: MRC mode of communication for uplink communication with that
SS. If not, the BS proceeds with the decision-making process. At
308, the BS determines if the SS is part of an orthogonal pair of
SSs. If not, the BS selects TX: CDD and RX: MRC mode of
communication for communication with that SS on the uplink. If the
SS is part of an orthogonal pair, the BS selects TX: CDD and RX:
SDMA communication mode for communication on the uplink. As
mentioned, orthogonality may be determined by uplink sounding
techniques.
[0029] Referring to FIG. 4, a preferred intelligent methodology of
selectively choosing a mode of downlink communication according to
system 100 is shown as method 400. Similar to the methods described
above, method 400 employs the intelligent algorithm described above
to select the optimum mode of communication between a BS and SS.
Accordingly, as will be further described, method 200 generally
involves determining SS mobility, SS distance, and SS
orthogonality. At 401, a BS, such as for example BS 101 shown in
FIG. 1, determines what modes are available for communication with
a number of SSs, such as for example SS 102-1 through 102-N as
shown in FIG. 1. BS 101 makes this determination based, in part, on
information received from SSs within its cell, relating to the
capabilities of those SSs.
[0030] At 402, BS 101 determines the number of transmit and/or
receive antennas associated with the SS. Based on that
determination, BS 101 eliminates one or more otherwise available
modes of communication for communication with that SS.
Specifically, BS 101 eliminates from selection those modes best
suited for SSs having multiple antennas where a SS has been
determined to have a singe antenna, and vice versa.
[0031] At 403, BS 101 determines if the SS is non-moving or
slow-moving, or fast-moving. According to a preferred embodiment,
what constitutes fast-moving will depend on system settings and can
be thought of in terms of a threshold set at BS 101. Based on that
determination, BS 101 may eliminate one or more otherwise available
modes of communication from selection.
[0032] At 404, BS 101 determines the relative position of the SS
within the cell. That is, BS 101 determines whether the SS is
closer to the cell boundary or closer to BS 101. Based on that
determination, BS 101 may eliminate one or more otherwise available
modes of communication from selection.
[0033] At 405, BS 101 determines orthogonality of the SS signal
with respect to at least one other SS signal. According to
particular embodiments, such a determination may involve
determining if the SS is part of an orthogonal pair of SSs. Based
on that determination, BS 101 may eliminate one or more otherwise
available modes of communication from selection.
[0034] At 406, once the intelligent methodology described above is
executed, there may be no more than one of the originally available
modes left for selection. However, in the event more than one of
the original modes of communication remains for selection, BS 101
may select a single mode based on a number of criteria such as, for
example, link reliability or implementation complexity. Also, each
mode may be prioritized according to one or more metrics, such that
BS 101 selects from the group of available modes according to the
priority of the available modes.
[0035] At 407, BS 101 reevaluates the mode of communication being
used to determine if that mode is still the optimal mode. This
reevaluation may be prompted by the passage of a predetermined time
interval as previously determined by BS 101, or may be prompted by
observation of one or more changes in relevant conditions. The
reevaluation process may prompt method 200 to begin at one of the
steps described above, such that the entire method 200 need not
necessarily be repeated.
[0036] Referring to FIG. 5, a specific implementation of method 400
is shown. In FIG. 5, generalized method 400 is implemented more
specifically as method 500 in a communication network operating
according to the WiMAX standard. According to this example, there
will likely be four available modes of communication: MIMO, STBC,
SDMA, MRC, and BF. At 501, a determination is made as to the number
of antennas associated with the SS. Of course, if it is determined
that the SS is equipped with only a single antenna, MIMO will not
be an available communication mode.
[0037] Proceeding along the "single antenna" decision making
process, at 502, it is determined if the SS is not-moving or
slow-moving, or fast-moving. SS velocity is preferably determined
sooner rather than later in the process because neither of BF,
SDMA, or 2.times.MIMO are well-suited for fast-moving SSs.
Therefore, determination of a fast-moving SS can typically
eliminate several otherwise available modes of communication
relatively quickly. If the SS is determined to be fast-moving, STBC
is selected as the downlink communication mode. STBC is chosen for
a fast-moving SS because it provides more reliability; that is,
STBC offers the fastest link performance. If the SS is determined
to be non-moving or slow-moving, the decision-making process
continues. At 503, it is determined whether the SS is closer to the
cell boundary or closer to the BS. Those SSs typically are
associated with a poor receiving signal or strong neighboring cell
interference. As such, if a SS is determined to be close to a cell
boundary, BF is selected as the downlink communication mode. In
this case, BF is chosen to increase signal strength while reducing
interference from other cells. Also, the present inventors have
recognized that it is less efficient to accommodate several users
at the cell boundary using the same resource, as doing so increases
interference. If the SS is determined to be closer to the BS than
the cell boundary, the decision-making process continues. At 504,
it is determined whether the SS is part of an orthogonal pair of
SSs. If not, BF is chosen as the downlink mode of communication. If
the SS is part of an orthogonal pair, SDMA is chosen as the
downlink mode of communication.
[0038] If, at 501, it is determined that there are multiple
antennas associated with the MS, the decision making process
proceeds along the multiple antenna, e.g., "dual antenna," decision
path. At 505, it is determined if the SS is not-moving or
slow-moving, or fast-moving. As mentioned above, SS velocity is
preferably determined sooner rather than later in the process
because neither of BF, SDMA, or 2.times.MIMO are well-suited for
fast-moving SSs. Therefore, determination of a fast-moving SS can
typically eliminate several otherwise available modes of
communication relatively quickly. If the SS is determined to be
fast-moving, TX: STBC RX: MRC is selected as the downlink
communication mode. STBC is chosen for a fast-moving SS because it
provides more reliability; that is, STBC offers the fastest link
performance. If the SS is determined to be non-moving or
slow-moving, the decision-making process continues. At 506, it is
determined whether the SS is closer to the cell boundary or closer
to the BS. As mentioned above, SSs near a cell boundary are
typically associated with a poor receiving signal or strong
neighboring cell interference. As such, if a SS is determined to be
close to a cell boundary, TX: BF, RX: MRC is selected as the
downlink communication mode. In this case, BF is chosen to increase
signal strength while reducing interference from other cells. Also,
the present inventors have recognized that it is less efficient to
accommodate several users at the cell boundary using the same
resource, as doing so increases interference. If the SS is
determined to be close to the BS, the decision-making process
continues. At 507, it is determined whether there is a
line-of-sight (LOS) condition. Specifically, a (LOS) condition is
detected by sampling input data for a predetermined time period,
comparing a magnitude of the sampled input data to a threshold
signal strength level, and asserting a LOS indication if the number
of samples that have signal strength less than the threshold signal
strength level is less than a predetermined value. If a LOS
condition is not detected, MIMO is selected as the downlink
communication mode. MIMO is selected because it is advantageously
used in a multi-path rich environment where local scatter signals
are present. LOS may be determined by determining the condition
number of the associated channel matrix. For example, assuming the
case of M Tx antenna and N Rx antenna, this will be an M.times.N
matrix. If a LOS condition is detected, the channel matrix will be
ill-conditioned, meaning the matrix condition will be above the
predetermined value described above. If a LOS condition is
detected, TX: SDMA RX: MRC is selected as the downlink
communication mode.
[0039] Referring again to FIG. 1, other embodiments of the present
invention can be examined. While embodiments described above
focused on communication in the context of a single BS and multiple
SSs; it should be appreciated that the concepts described herein
readily extend to communication in the context of multiple BSs and
multiple SSs. The concepts of cooperative transmission modes are
used to coordinate among multiples BSs associated with adjacent
cells and to utilize such coordination in selecting a communication
mode. In a multi-cell environment, BS 101 and BS 103 establish
communication parameters between one another to resolve, for
example, which SSs each BS will communicate with, whether the SSs
are operating in single or multiple antenna mode, interference
conditions, transmission schedules, and the like. For instance, if
the SS is determined to operate as a multiple antenna SS,
cooperative transmission MIMO can be employed where the
transmitting antennas associated with different BSs work together
as a "virtual" BS. These concepts are fully explained in U.S.
Patent Application Publication No. 2006/0120477, the disclosure of
which is herein incorporated by reference in its entirety. By way
of example, suppose BS 101 transmits a downlink communication,
e.g., AO, to SS 102-N, which is located along the cell boundary of
BS 101. BS 101 also transmits a signal, e.g., AI, to BS 103. In
response, BS 103 transmits the communication received from BS 101,
that is AI, to SS 102-N. BS 103 and BS 101 can communicate with one
another via the backhaul as known in the art, e.g., through the
combination of 107 and 108. At SS 102-N, signal AO is received from
BS 101 and signal AI is received from BS 103. SS 102-N
advantageously leverages the signals received from both BSs to
decode the full sequence, AOAI. This scheme, similar to a 2.times.2
MIMO scheme, is used to select from available communication modes
and benefits from the resources and measurements provided from each
of BS 101 and 103. As seen from the above, determinations relating
to the number of antennas associated with a SS, in combination with
cooperative transmission concepts, can be combined to provide an
communication mode selection scheme.
[0040] By way of further example, consider the cooperative
transmission mode scheme described above. Further consider that SS
102-N is subject to interference by, for example, communications
between BS 103 and SS 104-1. Similar to the discussion above, BS
101 and BS 103 establish communication parameters between one
another to resolve, for example, which SSs each BS will communicate
with, whether the SSs are operating in single or multiple antenna
mode, interference conditions, transmission schedules, and the
like. It follows that BS 101 and BS 103 will determine that SS
102-N is located at or near the cell boundary, and therefore,
subject to relatively strong interference from BS 103. If so, BS
103 pre-determines the signals that are transmitted between BS 103
and SS 104-1. Accordingly, BS 103 then notifies BS 101 as to the
signals communicated between BS 103 and SS 104-1. As described
above, such communication between BS 103 and BS 101 can be
accomplished through a network backbone, as known in the art. In
response, BS 101 "pre-cancels" the interfering signal (i.e., the
signal between BS 103 and SS 104-N) from its downlink communication
signal to SS 102-N. This technique is sometimes referred to as
"dirty paper coding" by those skilled in the art. These concepts
are fully explained in U.S. patent application Ser. No. 11/492,709,
the disclosure of which is herein incorporated by reference in its
entirety and attached hereto as Appendix A. In view of the above,
algorithms involving coordination among adjacent BSs, determination
of the number of antennas associated with a SS, determination of SS
position within a cell provide for a communication mode selection
scheme in the cooperative transmission context. As a result of the
coordination between BS 101 and BS 103, SS 102-N, at the cell
boundary of BS 101, receives downlink communication from BS 101
free from the interfering signal between BS 103 and SS 104-1.
[0041] As seen, utilizing cooperative transmission modes improves
system performance at the cell boundary by either increasing
throughput or reducing interference. Such embodiments are
facilitated by communication among BSs and during system initiation
where a BS will negotiate with other neighboring BSs for
communication capabilities, and the like.
[0042] According to another embodiment of the present invention,
the selection of a communication mode between BS and SS may be
based upon consideration of the upper layer QoS. That is, the
algorithms described herein are not limited to considering only
physical layer conditions, e.g., SS mobility, RSSI/CINR, and SS
orthogonality to make a decision. Rather, upper layer service
requirements may be considered for a more refined decision-making
process. For instance, consider a subscriber utilizing a
narrowband, real-time service (e.g., a voice call) which usually
does not allow for re-transmission/ARQ. In such case, a relatively
reliable mode, perhaps STBC, is more desirable for the subscriber.
One the other hand, consider the case where the subscriber instead
is static and downloading a relatively large data file that
requires high data transfer speed. In this case the user is more
likely tolerate delay for retransmission, etc. Accordingly, a more
aggressive or frequency-efficient scheme, perhaps MIMO or SDMA,
will provide a better choice. Further, to enable this joint
optimization, will ideally negotiate with SSs to exchange physical
layer information and to will also include higher level QoS
parameters.
[0043] Although the present invention and its advantages have been
described in detail, it should be understood that various changes,
substitutions and alterations can be made herein without departing
from the spirit and scope of the invention as defined by the
appended claims. Moreover, the scope of the present application is
not intended to be limited to the particular embodiments of the
process, machine, manufacture, composition of matter, means,
methods and steps described in the specification. As one of
ordinary skill in the art will readily appreciate from the
disclosure of the present invention, processes, machines,
manufacture, compositions of matter, means, methods, or steps,
presently existing or later to be developed that perform
substantially the same function or achieve substantially the same
result as the corresponding embodiments described herein may be
utilized according to the present invention. Accordingly, the
appended claims are intended to include within their scope such
processes, machines, manufacture, compositions of matter, means,
methods, or steps.
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