U.S. patent application number 11/421632 was filed with the patent office on 2007-12-06 for coordinating transmission scheduling among multiple base stations.
Invention is credited to Fang-Chen Cheng, Shupeng Li, Lei Song.
Application Number | 20070280175 11/421632 |
Document ID | / |
Family ID | 38683938 |
Filed Date | 2007-12-06 |
United States Patent
Application |
20070280175 |
Kind Code |
A1 |
Cheng; Fang-Chen ; et
al. |
December 6, 2007 |
COORDINATING TRANSMISSION SCHEDULING AMONG MULTIPLE BASE
STATIONS
Abstract
A method and an apparatus for scheduling transmissions of a
plurality of cells in a wireless communications system including
one or more base stations is provided. The method comprises
providing a set of virtual channels to enable an intra-cell
transmission orthogonal to another transmission within each cell of
the plurality of cells and inter-cell transmissions orthogonal to
other transmissions across a cluster of cells associated with the
one or more base stations. The method further comprises exchanging
signaling messages between two or more base stations to coordinate
scheduling of the intra-cell transmission with the inter-cell
transmissions for the cluster of cells. For optimizing a parameter
associated with scheduling of a plurality of users from a cluster
of cells in a wireless communication system, an optimal power level
for the parameter of each active user may be searched to maximize
an indication of system capacity of the wireless communication
system. This enables a coordinated jointly scheduling of the users
active in the cluster of cells based on the optimal power levels
such that the total interference within the cluster may be
minimized to maximize the system throughput/capacity.
Inventors: |
Cheng; Fang-Chen; (Randolph,
NJ) ; Li; Shupeng; (Edison, NJ) ; Song;
Lei; (Randolph, NJ) |
Correspondence
Address: |
WILLIAMS, MORGAN & AMERSON
10333 RICHMOND, SUITE 1100
HOUSTON
TX
77042
US
|
Family ID: |
38683938 |
Appl. No.: |
11/421632 |
Filed: |
June 1, 2006 |
Current U.S.
Class: |
370/338 |
Current CPC
Class: |
Y02D 70/122 20180101;
Y02D 70/146 20180101; H04W 72/1278 20130101; Y02D 70/1262 20180101;
Y02D 70/144 20180101; Y02D 70/164 20180101; H04B 7/022 20130101;
H04W 16/10 20130101; Y02D 70/1244 20180101; Y02D 70/442 20180101;
Y02D 70/142 20180101; Y02D 70/1242 20180101; Y02D 30/70
20200801 |
Class at
Publication: |
370/338 |
International
Class: |
H04Q 7/24 20060101
H04Q007/24 |
Claims
1. A method for scheduling transmissions of a plurality of cells in
a wireless communications system including one or more base
stations, the method comprising: providing a set of channels to
enable an intra-cell transmission orthogonal within each cell of
said plurality of cells and inter-cell transmissions orthogonal
across a cluster of cells associated with said one or more base
stations; and coordinating scheduling of said intra-cell
transmission with said inter-cell transmissions for said cluster of
cells between at least two base stations of said base stations.
2. A method, as set forth in claim 1, wherein coordinating
scheduling of said intra-cell transmission with said inter-cell
transmissions further comprises: exchanging signaling messages
between said at least two base stations.
3. A method, as set forth in claim 1, wherein coordinating
scheduling of said intra-cell transmission with said inter-cell
transmissions further comprises: managing one or more radio
resources of said one or more base stations in real time to jointly
schedule said intra-cell transmission with said inter-cell
transmissions of said cluster of cells, wherein said set of
channels being virtual channels having an orthogonality property
effective to reduce interference among said intra-cell and
inter-cell transmissions; and controlling interference between said
cluster of cells jointly to optimize an overall performance
parameter of said wireless communications system.
4. A method, as set forth in claim 3, wherein controlling
interference between said cluster of cells jointly further
comprises: minimizing a parameter associated with a source
responsible for generating said interference between said cluster
of cells.
5. A method, as set forth in claim 2, wherein managing one or more
radio resources of said one or more base stations in real time
further comprises: transforming an indication of the transmitted
power into a diversity gain.
6. A method, as set forth in claim 1, further comprising: using a
set of virtual channels to provide said set of channels; and
partitioning said set of virtual channels by at least one of time,
frequency, space, antenna, and codes for said cluster of cells.
7. A method, as set forth in claim 6, wherein partitioning said set
of virtual channels further comprises: dynamically partitioning a
resource of said set of virtual channels in real time to adapt a
channel variation of each user and an indication of user mobility
within said cluster of cells.
8. A method, as set forth in claim 6, further comprising:
supporting at least one of a diversity combining or soft-handover
for users of said cluster of cells in a High-Speed Packet Access
interface to cause one or more sources of an inter-cell
interference for each user to provide a signal enhancement in a
handover region.
9. A method, as set forth in claim 8, further comprising: providing
a macro diversity gain in each received signal on a physical
channel of a High-Speed Packet Access interface for said set of
virtual channels from each cell of said cluster of cells that is
associated with said at least one of diversity combining or
soft-handover.
10. A method, as set forth in claim 6, further comprising:
supporting macro-diversity coherent combining in an Orthogonal
Frequency Division Multiple Access interface to mitigate one or
more sources of co-channel interference to a diversity transmission
from a neighboring cell of said cluster of cells.
11. A method, as set forth in claim 8, wherein supporting
macro-diversity coherent combining in an Orthogonal Frequency
Division Multiple Access interface further comprises: scheduling
substantially the same set of data transmission of each sub-channel
from each cell of said cluster of cells for a user.
12. A method, as set forth in claim 11, further comprising:
coordinating a joint assignment of said each sub-channel for each
cell of said cluster of cells.
13. A method, as set forth in claim 1, further comprising: fetching
user information of a radio resource characteristic for each user
and an indication of cross correlation between said cluster of
cells to manage overall interference for said cluster of cells; and
coordinating control and virtual channel assignment between said
cluster of cells by delivering control information and an
indication of interference to each base station of said one or more
base stations with a time stamp based on said user information and
said indication of cross correlation.
14. A method, as set forth in claim 13, further comprising:
distributing a joint scheduler in said one or more base stations
for scheduling a virtual channel of said set of virtual channels
for each user and to interconnect said one or more base stations
with a virtual interconnect; using high-speed communication links
between said one or more base stations to enable said joint
scheduler to collect feedback information and user information from
each base station of said one or more base stations; and assigning
said virtual channel of said set of virtual channels to each user
in said cluster of cells based on said feedback information and
said user information.
15. A method, as set forth in claim 14, wherein coordinating
control and virtual channel assignment between said cluster of
cells further comprises: using a common reference time among said
cluster of cells for the reference of control information and to
manage overall interference for said cluster of cells.
16. A method, as set forth in claim 15, wherein using a common
reference time among said cluster of cells further comprises:
synchronizing said high-speed communication link and said virtual
interconnect between said one or more base stations based on at
least one of a system and frame counter.
17. A method, as set forth in claim 1, further comprising: using a
client-server architecture based joint scheduling control for
jointly assigning a corresponding virtual channel of said set of
virtual channels to each user in said cluster of cells.
18. A method, as set forth in claim 17, wherein using a
client-server architecture based joint scheduling control further
comprises: enabling a virtual scheduler for said one or more base
stations each being a client to a dedicated scheduling server for
jointly controlling scheduling of radio resources in said wireless
communication system and managing overall interference of said
wireless communication system for said cluster of cells;
19. A method, as set forth in claim 18, further comprising:
collecting feedback and user information from said cluster of cells
as an input to said virtual scheduler.
20. A method for, as set forth in claim 19, further comprising:
assigning said corresponding virtual channel of said set of virtual
channels to each user in said cluster of cells based on said
feedback and user information to minimize said overall interference
and maximize throughput of said wireless communication system.
21. A method for optimizing a transmission parameter associated
with scheduling of a plurality of users from a cluster of cells in
a wireless communication system, the method comprising: searching
an optimal power assignment for said transmission parameter of each
user of said plurality of users to maximize an indication of system
capacity of said wireless communication system; and jointly
scheduling said plurality of users active in said cluster of cells
based on said optimal power assignments.
22. A method, as set forth in claim 21, wherein jointly scheduling
said plurality of users active in said cluster of cells further
comprises: scheduling each user in said cluster of cells based on
an optimization of power level as an objective function being the
sum of the Shannon capacity of said plurality of users in said
cluster of cells.
23. A method, as set forth in claim 21, wherein searching an
optimal power level for said parameter of each user of said
plurality of users further comprises: using a parameter
optimization algorithm to search for a sub-optimal solution of a
resource for each user in said cluster of cells.
Description
FIELD OF THE INVENTION
[0001] This invention relates generally to telecommunications, and
more particularly, to wireless communications.
DESCRIPTION OF THE RELATED ART
[0002] In multi-user network environments, since many users desire
access to network resources, scheduling is a useful technique to
determine a way in which users may access the network resources. In
many wireless communication systems, for instance, multiple users
access a common access medium. A scheduling algorithm typically
determines allocation of a channel to provide each user access to
the common access medium with minimal interference to other users.
The scheduling algorithm in a communication network may determine
an efficient use of network resources, for example, to maximize
network throughput.
[0003] As multiple users seek access to a network, a scheduler may
provide access that maximizes network throughput with a desired
Quality of Service (QoS) for communications. For example, in a
wireless communications network, a base station controller (BSC) or
a radio network controller (RNC) may schedule reverse link (RL) or
uplink (UL) communications from the mobile stations to the base
stations. Alternatively, a base station may schedule forward link
(FL) or downlink (DL) communications in adjacent cells serviced by
other base stations. A mobile station in a handoff communicates
with two or more base stations as it transitions from one base
station to another, affecting the scheduling of the communications
therebetween. For scheduling a data packet transmission on a
reverse link from a mobile station, a base station indicates a data
rate, a radio resource and a corresponding power level that may
reduce interference from such communications.
[0004] Wireless communication systems have been evolving from the
1.sup.st generation analog cellular systems (Advanced Mobile Phone
System (AMPS) system) to the 2.sup.nd generation digital cellular
systems (CDMA One, TDMA and Global System for Mobile communications
(GSM)) to the 3.sup.d generation digital multimedia systems
(CDMA2000 1.times. and Universal Mobile Telecommunications System
(UMTS)) to the high-speed data system (CDMA2000 Evolution-Data
Optimized (EV-DO) and UMTS High-Speed Downlink Packet Access
(HSDPA)/Enhanced Dedicated Channel (E-DCH)).
[0005] While the 3.sup.rd generation wireless system can support
multimedia service with a desired Quality of Service (QoS), the
efficiency of the 3.sup.rd generation wireless system for robust
data transmission is not that high since the system is a
circuit-switching type system. On the other hand, a packet
switching type high-speed data system uses efficient radio resource
sharing and scheduling with radio channel awareness in the
transmission. Such scheduling coordinates the shared access based
on the feedback of individual radio channel conditions. By
scheduling the transmission in favor of the good channel users at
any short time interval, the fast scheduling approach improves the
system data throughput. In order to respond to varying radio
channel conditions for providing relatively high efficient data
transmission, scheduling and resource management functions have
been relocated to the base stations. For example, downlink radio
resources in both the temporal domain and the frequency domain may
be controlled by a scheduler in the base station. A scheduling
algorithm may assign one or more channels or sub-channels to the
mobile station. Resource allocation typically includes determining
powers and/or bandwidth to optimize performance within the cell
served by the base station.
[0006] Many high-speed packet switching systems, including HSDPA
and E-DCH, focus on the optimization of the shared access control
of the transmitted time, power, data rate, overall system rise over
thermal (RoT) and physical layer forms of users in the same cell.
The optimization of the shared access control relates to control of
an interference source. When a shared access control is applied
within a cell only, the cross interference (inter-cell
interference) to the other cell is generated proportionally to the
signal strength for the intra-cell. This interference limits the
ability to improve overall system signal-to-noise ratio (SNR) and
spectral efficiency. Spectral efficiency is a measure of the
performance of encoding to transmit bits at a given data rate using
bandwidth based on an encoding method that codes information.
[0007] Generally, interference management may be categorized into
three classes, namely interference avoidance, interference
coordination, and interference mitigation. Interference avoidance
involves creating a strategy and executing it independently at each
cell for shared access control to reduce the interference with each
other. Interference coordination coordinates the strategy between
cells for further suppressing the potential interference. By
jointly transmitting between cells, interference mitigation reduces
the potential interference between the cell served by the base
station and adjacent cells.
[0008] More specifically, the interference avoidance or
coordination schemes suppress the cross interference by creating an
orthogonal set in time (time sharing) or frequency (frequency
reuse). Management of the transmitted power and synchronization
between the nodes, such as the base stations may reduce the cross
interference. The interference avoidance or coordination schemes
control the interference level to meet the desired QoS levels of
each service. However, the time/frequency sharing or transmitted
power management strategy does not improve the spectral
efficiency.
[0009] Interference mitigation schemes may also be implemented to
reduce interference between the cell served by the base station and
adjacent cells. For example, base stations in adjacent cells may
transmit using the same set of frequency channels. If both base
stations allocate the same frequency channel to different mobile
units, then the mobile units may receive a composite signal
including signals from both base stations on the assigned frequency
channel. One portion of the composite signal is the desired signal
and another portion of the composite signal will be seen as
interference, which is conventionally referred to as "inter-cell
interference." Inter-cell interference may interfere with, and
potentially disrupt, communication with the mobile units. Thus,
interference mitigation schemes typically minimize inter-cell
interference by coordinating assignment of the radio channels, and
the power assigned to each channel, among base stations that serve
adjacent cells.
[0010] In wireless communications, some interference is also caused
by lack of the coordination between the transmissions and resource
management. Many cellular communication systems manage the
interferences and noise through cell planning, interference
coordination, interference avoidance, transmitted power control,
transmitted rate adaptation or radio resource management schemes.
Some interference management schemes adapt radio resources based on
the level of the interference received and the tolerable
interference to meet its QoS requirement. Fast communication links
between the nodes and a large-scale radio resource management in
real time enables control of the transmission based on a relatively
fast radio channel feedback through an air interface and
coordinates the transmission between cells for the interference
management. To improve system performance, a high-speed wireless
access system adapts communication links between the nodes or base
stations. However, signal-to-interference ratio (SIR) limits the
link adaptation because interference limits the SIR caused by a
neighboring system. For providing interference management, a
high-speed data system, such as a UMTS HSDPA/E-DCH system,
incorporates a relatively fast feedback of the radio channel
condition and transmission rate adaptation. However, such a passive
interference management provides a limited gain on system
performance and the spectral efficiency. Moreover, both the
wideband CDMA (W-CDMA) and HSDPA systems being passive in
interference management may not provide a desired system
performance and the spectral efficiency.
[0011] Several access technologies use aggressive interference
management schemes. Two examples of the aggressive interference
management schemes include CDMA interference cancellation (or UL
multi-user detection) and the pre-coding techniques. The
interference cancellation scheme estimates the interference at the
receivers and subtracts the re-encode interference into the
received signals for further demodulation. However, the
interference cancellation technique is limited by the estimated
accuracy of the interference at a receiver, which is determined by
the received signal to noise ratio. The pre-coding technique
integrates the estimated interference into the channel coding of a
transmitted signal to minimize the interference at the receiver
side. However, the required knowledge of the channel response in
real time for the channel coding limits the pre-coding technique.
Accordingly, both the interference cancellation and pre-coding
techniques have severe consequences of performance degradation if
the estimated interference is inaccurate because the estimated
errors in the planned removal of the interference introduce other
sources of interference.
SUMMARY OF THE INVENTION
[0012] The following presents a simplified summary of the invention
in order to provide a basic understanding of some aspects of the
invention. This summary is not an exhaustive overview of the
invention. It is not intended to identify key or critical elements
of the invention or to delineate the scope of the invention. Its
sole purpose is to present some concepts in a simplified form as a
prelude to the more detailed description that is discussed
later.
[0013] The present invention is directed to overcoming, or at least
reducing, the effects of, one or more of the problems set forth
above.
[0014] In one embodiment of the present invention, a method is
provided for scheduling transmissions of a plurality of cells in a
wireless communications system including one or more base stations.
The method comprises providing a set of channels to enable an
intra-cell transmission orthogonal within each cell of the
plurality of cells and inter-cell transmissions orthogonal across a
cluster of cells associated with the one or more base stations. The
method further comprises coordinating scheduling of the intra-cell
transmission with the inter-cell transmissions for the cluster of
cells between at least two base stations of the one or more base
stations.
[0015] In yet another embodiment, a method is provided for
optimizing a parameter associated with scheduling of a plurality of
users from a cluster of cells in a wireless communication system.
The method comprises searching an optimal power level for the
parameter of each user of the plurality of users to maximize an
indication of system capacity of the wireless communication system.
The method further comprises jointly scheduling the plurality of
users active in the cluster of cells based on the optimal power
levels.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The invention may be understood by reference to the
following description taken in conjunction with the accompanying
drawings, in which like reference numerals identify like elements,
and in which:
[0017] FIG. 1 schematically depicts a wireless communications
system, such as a Long Term Evolution (LTE) UMTS system which
includes first and second base stations and a joint virtual
scheduler for scheduling transmissions of a plurality of cells in a
relatively high-speed wireless access network according to one
illustrative embodiment of the present invention;
[0018] FIG. 2 schematically depicts an architecture of joint
scheduling for the Long Term Evolution (LTE) UMTS system in which
the joint virtual scheduler shown in FIG. 1 may find application in
accordance with one illustrative embodiment of the present
invention;
[0019] FIG. 3 depicts a stylized representation for implementing a
method that may use a set of virtual channels for active users and
signaling messages between the base stations to coordinate a joint
scheduling of inter-cell transmission with intra-cell transmissions
for a cluster of cells in the wireless communications system shown
in FIG. 1 consistent with an exemplary embodiment of the present
invention;
[0020] FIG. 4 illustrates a stylized representation for
implementing a method of scheduling power in frequency domain for
the transmissions from the base stations to the active Access
Terminals in the cluster of cells to maximize the total throughput
or capacity for each base station shown in FIG. 1, according to one
embodiment of the present invention; and
[0021] FIG. 5 illustrates a stylized representation for
implementing a method of scheduling power in time domain for the
transmissions from the base stations to the active Access Terminals
in the cluster of cells to maximize the total throughput or
capacity for each base station shown in FIG. 1, according to one
illustrative embodiment of the present invention.
[0022] While the invention is susceptible to various modifications
and alternative forms, specific embodiments thereof have been shown
by way of example in the drawings and are herein described in
detail. It should be understood, however, that the description
herein of specific embodiments is not intended to limit the
invention to the particular forms disclosed, but on the contrary,
the intention is to cover all modifications, equivalents, and
alternatives falling within the spirit and scope of the invention
as defined by the appended claims.
DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS
[0023] Illustrative embodiments of the invention are described
below. In the interest of clarity, not all features of an actual
implementation are described in this specification. It will of
course be appreciated that in the development of any such actual
embodiment, numerous implementation-specific decisions may be made
to achieve the developers' specific goals, such as compliance with
system-related and business-related constraints, which will vary
from one implementation to another. Moreover, it should be
appreciated that such a development effort might be complex and
time-consuming, but may nevertheless be a routine undertaking for
those of ordinary skill in the art having the benefit of this
disclosure.
[0024] Generally, a method and an apparatus are provided for
coordinating transmission scheduling among multiple access nodes or
base stations. By using relatively fast communication between the
access nodes or base stations and resource management in real time,
a Universal Mobile Telephone System (UMTS) Long Term Evolution
(LTE) may control the transmission based on fast radio channel
feedback through an air interface and coordinate the transmission
between cells for managing interference. In particular, a joint
scheduler may manage one or more radio resource of all base
stations in a cluster in real time and jointly control the
interference to optimize the overall system performance. By using
radio resource management and interference mitigation, the joint
scheduler may maximize the signal-to-noise ratio of a received
signal and thus improve the system spectral efficiency. The joint
scheduler may jointly coordinate the transmissions of cells in a
cluster to minimize the overall interference. By jointly
coordinating communications of the cells in the cluster together,
the joint scheduler may mitigate interference from the other
neighboring cells and provide a signal strength enhancement
instead. The interference management may minimize the generation of
the interference and the transmitted power may be transformed into
a gain, which increases the spectral efficiency and may enhance
system capacity for each cell with universal reuse. To this end,
the joint scheduler may create a super set of orthogonal virtual
channels across all the cells in the cluster. The interference
mitigation may enhance the signal-to-noise ratio of the received
signal. The super virtual channel set comprises a set of virtual
channels that may be used in each cell with universal reuse. Since
the virtual channels in the super virtual channel set are
orthogonal to each other within the same cell and across the cells,
the super virtual channel set for all cells in the cluster enable
the transmission to be orthogonal to each other (intra and inter)
cells. This orthogonal inter-cell and intra-cell transmission may
minimize the total interference within the cluster. The joint
scheduler may support multiple access schemes and underlying
physical layer forms. The optimization of the system performance
for different multiple access schemes and underlying physical layer
forms may be based on information available for optimization. The
joint scheduler may not rely upon ideal knowledge or feedback of a
radio channel condition.
[0025] FIG. 1 schematically depicts a wireless communications
system, such as a Universal Mobile Telephone System (UMTS) Long
Term Evolution (LTE) 100 which includes first and second base
stations 105(1, 2) and a joint virtual scheduler 108 for scheduling
transmissions of a plurality of geographic areas or cells 110 (1-m)
in a relatively high-speed wireless access network 115 according to
one illustrative embodiment of the present invention. Each base
station of the first and second base stations 105(1, 2) may service
one or more of the cells 110 (1-m). By using one or more of the
base stations 105(1, 2), multiple Access Terminals 120(1, 2) and
125(1) (ATs, also known as User Equipment (UE), mobile stations,
and the like) active within the cells 110 (1-m) may then access the
high-speed wireless access network 115 and other interconnected
telecommunications systems, such as a publicly switched telephone
system (PSTN) and a Data network. To provide wireless connectivity
to the Access Terminals 120(1, 2) and 125(1), the base stations
105(1, 2), in turn, may communicate with a Server 122 that connects
the cells 110(1-m) to the UMTS Long Term Evolution system 100.
[0026] For illustrative purposes, the wireless communications
system of FIG. 1 is the UMTS Long Term Evolution system 100,
although it should be understood that the present invention may be
applicable to other systems that support data and/or voice
communication. The UMTS Long Term Evolution system 100 has some
similarities to a conventional UMTS system, but differs
substantially with respect to the operation of the instant
invention with regard to the first and second base stations 105(1,
2). That is, in the UMTS Long Term Evolution system 100, the joint
virtual scheduler 108 may be either functionally deployed at a
server to coordinate scheduling of the transmissions for a cluster
110a of cells in a relatively centralized manner, or alternatively,
distributed to the base stations 105(1, 2). However, instead of
scheduling transmissions of a single cell or adjacent cells, the
joint virtual scheduler 108 may jointly schedule transmissions for
the cluster 110a of cells in which multiple active users may be
seeking access to a shared resource of the high-speed wireless
access network 115.
[0027] Thus, it should be appreciated that a coordinated joint
virtual scheduling scheme for the UMTS Long Term Evolution system
100 may be useful in at least two instances. First, to reduce the
intra-cell interference within a cell 110 of the cluster 110a of
cells jointly with the inter-cell interference caused by
transmissions of adjacent or nearby cells in the cluster 110a of
cells, and second, during hand-offs of the ATs 120 from one base
station to another base station of the first and second base
stations 105(1, 2). The coordinated joint virtual scheduling scheme
may support a diversity combining and/or soft-handover for active
users of the cluster 110a of cells in a High-Speed Packet Access
interface. The coordinated joint virtual scheduling scheme may
cause one or more sources of an inter-cell interference for each
user to provide a signal enhancement in a handover region. For
example, the coordinated joint virtual scheduling scheme may
provide a macro diversity gain in each received signal on a
physical channel of the High-Speed Packet Access interface for a
set of channels, such as virtual channels 145 from each cell of the
cluster 110a of cells that is associated with the diversity
combining and/or soft-handover.
[0028] The UMTS Long Term Evolution system 100 and the Server 122
may operate according to Universal Mobile Telecommunication
Services (UMTS) protocols and may implement Orthogonal Frequency
Division Multiple Access (OFDMA). However, persons of ordinary
skill in the art having benefit of the present disclosure should
appreciate that the present invention is not limited to
communication systems that operate according to UMTS and/or OFDMA.
In alternative embodiments, the UMTS Long Term Evolution system 100
may operate according to one or more other protocols including, but
not limited to, the Global System for Mobile communication (GSM),
Code Division Multiple Access (CDMA, CDMA 2000), and the like.
[0029] Specifically, each base station of the first and second base
stations 105(1, 2) may provide the wireless connectivity to the
Access Terminals 120(1, 2) and 125(1) according to any desirable
protocol, including a Code Division Multiple Access (CDMA,
cdma2000) protocol, an Evolved Data Optimized (EVDO, 1.times.EVDO)
protocol, a Universal Mobile Telecommunication System (UMTS)
protocol, a Global System for Mobile communications (GSM) protocol,
and like. The cdma2000 1.times.EV-DO specification uses the term
"access network" for a base station, and "access terminal" for a
mobile station, however, in the illustrated embodiment, the access
network 115 is shown separate from the base stations 105(1, 2).
[0030] Examples of the Access Terminals 120(1, 2) and 125(1) may
include a host of wireless communication devices including, but not
limited to, cellular telephones, personal digital assistants
(PDAs), and global positioning systems (GPS) that employ a spread
spectrum communications system to operate in the high-speed
wireless data network 120, such as a digital cellular CDMA network.
Other examples of the Access Terminals 120(1, 2) and 125(1) may
include smart phones, text messaging devices, and the like.
[0031] In the UMTS Long Term Evolution system 100, the high-speed
wireless access network 115 may deploy any desirable protocol to
enable wireless communications between the first and second base
stations 105(1, 2) and the Access Terminals 120(1, 2) and 125(1)
according to any desirable protocol. Examples of such a protocol
include a (CDMA, cdma2000) protocol, an Evolved Data Optimized
(EVDO, 1.times.EVDO) protocol, a UMTS protocol, a GSM protocol, and
like.
[0032] Other examples of such a protocol include a 1.times.EV-DO
protocol, a UMTS protocol, a GSM protocol, and like. The 3G
cellular systems based on any one of these protocols, or the like,
provide enhanced voice capacity and support high data rate packet
based services. As one example, these features are provided in
cdma2000 1.times.EV high rate packet data air interface referred to
as IS-856. More specifically, the 3G cellular system cdma2000
1.times.EV provides high-speed wireless Internet access to users
with asymmetric data traffic relative to a cellular network based
on IS-95 standard. For example, data rate of an active user at the
Access Terminal 120(1) may very from 9.6 kbps to 153.6 kbps.
[0033] The base stations 105(1, 2) may be assigned a plurality of
channels within a frequency spectrum over which to communicate with
the Access Terminals 120(1, 2) and 125(1). The Access Terminal
120(1) within range of both the first and base stations 105(1, 2)
may communicate therewith using these channels. In this way, the
base stations 105(1, 2) may provide wireless connectivity to
corresponding geographical areas or cells 110(1-m). As discussed
above, the base stations 105(1, 2) may provide wireless
connectivity according to UMTS protocols and may implement OFDMA,
but the base stations 110 are not limited to these protocols. In
the illustrated embodiment, the first base station 105(1) provides
wireless connectivity to the Access Terminals 120(1, 2) and the
second base station 105(2) provides wireless connectivity to the
Access Terminals 125(1). However, persons ordinary skill in the art
having benefit of the present disclosure should appreciate that the
base stations may provide wireless connectivity to any number of
Access Terminals at any location within or proximate to the cells
110(1-m).
[0034] While the first base station 105(1) may provide one or more
intra-cell transmissions (TXs) 130(1, 2) with the Access Terminals
120(1, 2), respectively, the second base station 105(2) may provide
one or more intra-cell transmissions 135(1) with the Access
Terminal 125(1) and one or more inter-cell transmissions (TXs)
135(2) with the Access Terminal 120(1). In the illustrated
embodiment, the inter-cell and intra-cell transmissions 130, 135
include one or more channels within a selected frequency band,
e.g., the sub-carriers may be defined according to an OFDMA scheme.
Persons of ordinary skill in the art should appreciate that
sub-carriers may also be referred to using terms such as frequency
channels, sub-channels, tones, and the like.
[0035] To jointly schedule transmissions for the cluster 110a of
cells, the joint virtual scheduler 108 may comprise a parameter
optimization algorithm 140 that determines power assignments for
active users in the cluster 110a of cells. Based on a given maximum
power constraint of each base station 105, the parameter
optimization algorithm 140 determines transmit power from the base
stations 105 to the Access Terminal 120 or 125 on a particular
channel or sub-channel such that the total throughput/capacity of
the UMTS Long Term Evolution system 100 is maximized and co-channel
interference is minimized.
[0036] In the CELL_1 110(1), the base station 105(1) may use
different channels for intra-cell transmissions (TXs) 130(1, 2) to
transmit information to the Access Terminals 120(1, 2) at a
corresponding power assignment indicated by the parameter
optimization algorithm 140. However, the intra-cell transmission
135(1) to the Access Terminal 125(1) and the inter-cell
transmission 135(2) to the Access Terminal 120(1) from the base
station 105(1) in the cell CELL_2 110(2) may be jointly scheduled
with the CELL_1 110(1). That is, the base station 105(1) in the
cell CELL_2 110(2) of the cluster 110a of cells may utilize the
same channel for the inter-cell transmission 135(2) to the Access
Terminal 120(1) that the base station 105(1) may be using for one
of the intra-cell transmissions 130(1, 2) without increasing
inter-cell interference. To optimize an overall performance
parameter, e.g., the system throughput/capacity of the UMTS Long
Term Evolution system 100, the parameter optimization algorithm 140
may control interference between the cluster 110a of cells jointly
by minimizing a source parameter responsible for generating the
interference between the cluster 110a of cells.
[0037] By managing one or more radio resources, such as transmit
power of the base stations105 (1, 2) in real time, the joint
virtual scheduler 108 may jointly schedule the intra-cell
transmissions 130(1, 2) and 135(1) along with the inter-cell
transmission 135(2) of the cluster 110a of cells. As one example,
the parameter optimization algorithm 140 may transform an
indication of the transmitted power into a diversity gain.
Accordingly, power of the inter-cell and intra-cell transmissions
130, 135 on the channels may be scheduled in a manner that
mitigates inter-cell and/or intra-cell interferences.
[0038] In cellular communications, besides a radio channel or
frequency used for signal transmission, a virtual channel is used
to integrate multiple, disparate channels, for example, to collect
the feedback for analysis at a single location. The virtual channel
in 1.sup.st generation is a narrow band frequency carrier (FDMA)
with frequency reuse pattern between cells. The 2.sup.nd generation
GSM system has a virtual channel in time slot (TDMA) with frequency
reuse pattern between cells. The FDMA and TDMA type virtual
channels rely on the operation in separation of frequency/time. The
frequency reuse pattern controls the co-channel interference from
the same frequency at the time during the cell planning. The
interference management in the frequency reuse planning considers
the static worst-case scenario at the cell edge as the target.
[0039] The 3.sup.rd generation wideband CDMA (W-CDMA) system uses
the spreading code (or channelization code) as the virtual channel
with the universal frequency reuse by masking with different
scrambling code for each cell. While the downlink (DL) W-CDMA
channels are orthogonal to each other in code space within a cell
110, the uplink (UL) W-CDMA channels are non-orthogonal to each
other since the user mobility prevents synchronous receptions among
all users. In the W-CDMA system, control of the transmitted power
provides the interference management as a power control function
manages both the intra-cell and inter-cell interference. However,
such a power control does not affect the interference.
[0040] In the DL HSDPA system, the virtual channel is partitioned
in both code space and time space. The virtual channel in the HSDPA
system is assigned by a scheduler to maximize the data throughput
at a Transmission Time Interval (TTI) interval by quickly
responding to radio channel measurement feedback. The use of a
shorter TTI interval, such as 2 ms, the HSDPA system enables higher
speed transmission in a physical layer. Since the virtual channels
are orthogonal to each other within the cell 110 in the HSDPA
system, the interference management minimizes the inter-cell
interference based on the transmitted power assignment.
[0041] In operation, the joint virtual scheduler 108 may provide a
set of virtual channels 145 to enable the intra-cell transmissions
130(1, 2) and 135(1) orthogonal within each cell 110 of the
plurality of cells 110(1-m) and the inter-cell transmission 135(2)
orthogonal across the cluster 110a of cells associated with the
base stations 105(1, 2). The parameter optimization algorithm 140
may partition the set of virtual channels 145 by time, frequency,
space, antenna, and/or codes for the cluster 110a of cells. For
example, a dynamic partitioning of a resource of the set of virtual
channels 145 in real time may adapt a channel variation of each
user and an indication of user mobility within the cluster 110a of
cells.
[0042] To coordinate scheduling of the intra-cell transmissions
130(1, 2) and 135(1) with the inter-cell transmission 135(2) for
the cluster 110a of cells, the base stations 105(1, 2) may exchange
signaling messages (SIG_MSG) 150(1, 2) therebetween. As described
below, the joint virtual scheduler 108 may use the signaling
messages 150(1, 2) between the base stations 105(1, 2) to
coordinate scheduling of the inter-cell transmission 135(2) with
intra-cell transmissions 130(1, 2) and 135(1) for the cluster 110a
of cells.
[0043] Consistent with one embodiment, the joint virtual scheduler
108 may be distributed in the base stations 105(1, 2) for
scheduling a virtual channel of the set of virtual channels 145 for
each user and to interconnect the base stations 105(1, 2) with a
virtual interconnect. The virtual interconnect may comprise first
and second scheduling channels (SC_CH) 155(1, 2) and first and
second feedback channels (FB_CH) 160(1, 2). The joint virtual
scheduler 108 may communicate power assignments for active users to
the first base station 105(1) over the first scheduling channel
(SC_CH) 155(1) and receive feedback over the first feedback channel
(FB_CH) 160(1). Likewise, the second base stations 105(2) may
receive power assignments for active users over the second
scheduling channel (SC_CH) 155(2) and receive feedback over the
second feedback channel (FB_CH) 160(2).
[0044] By using a high-speed communication link 170(1) between the
base stations 105(1, 2), the joint virtual scheduler 108 may
collect feedback information and user information from each base
station. Based on the feedback information and user information,
the joint virtual scheduler 108 may assign a virtual channel of the
set of virtual channels 145 to each user in the cluster 110a of
cells. In particular, the joint virtual scheduler 108 may fetch the
user information of a radio resource characteristic for each user
and determine an indication of cross correlation between the
cluster 110a of cells to manage overall interference for the
cluster 110a of cells.
[0045] The joint virtual scheduler 108 may coordinate control and
virtual channel assignment between the cluster 11a of cells by
delivering control information and an indication of interference to
each base station of the base stations 105(1, 2) with a time stamp
based on the user information and the indication of cross
correlation. The joint virtual scheduler 108 may use a common
reference time among the cluster 110a of cells for the reference of
the control information and to manage overall interference for the
cluster 110a of cells. To use a common reference time among the
cluster 110a of cells, the joint virtual scheduler 108 may
synchronize the high-speed communication link 170(1) and the
virtual interconnect between the base stations 105(1, 2) based on a
system and/or a frame counter.
[0046] According to an alternate embodiment, a client-server
architecture based joint scheduling control may jointly assign a
corresponding virtual channel of the set of virtual channels 145 to
each user in the cluster 110a of cells. For jointly controlling
scheduling of radio resources in the UMTS Long Term Evolution
system 100 and managing overall interference thereof for the
cluster 110a of cells, in this exemplary embodiment, the joint
virtual scheduler 108 may treat each base station 105 as a client
for a dedicated scheduling server. The dedicated scheduling server
may collect feedback and user information from the cluster 110a of
cells as an input to the joint virtual scheduler 108.
[0047] In an Orthogonal Frequency Division Multiple Access (OFDMA)
interface, however, the coordinated joint virtual scheduling scheme
may support macro-diversity coherent combining to mitigate one or
more sources of co-channel interference to a diversity transmission
from the neighboring cell 110(m) of the cluster 110a of cells. The
coordinated joint virtual scheduling scheme may schedule
substantially the same set of data transmission of each sub-channel
from each cell of the cluster 110a of cells for a user and/or
coordinate a joint assignment of such sub-channels.
[0048] FIG. 2 schematically depicts an architecture 200 of joint
scheduling for the UMTS Long Term Evolution system 100 in which the
joint virtual scheduler 108 shown in FIG. 1 may find application in
accordance with one illustrative embodiment of the present
invention. By using the architecture 200 of joint scheduling, the
UMTS Long Term Evolution system 100 may not only control the
intra-cell transmissions 130(1, 2) and 135(1) based on radio
channel feedback through an air interface but also coordinate the
inter-cell transmission 135(2) between the cluster 110a of cells
for providing an interference management. The joint virtual
scheduler 108 may manage a radio resource of all the base stations
115(1, 2) within the cluster 110a of cells in real time to jointly
control the intra-cell and inter-cell interference for optimizing
the overall system performance by such interference mitigation.
This combined radio resource management and interference mitigation
may maximize the signal-to-noise (SNR) ratio of a received signal,
and thus, improve the system spectral efficiency.
[0049] The architecture 200 of joint scheduling may support a
plurality of multiple-access schemes 205 to provide each user
access to a common access medium without interference to other
users. Examples of the plurality of multiple-access schemes 205
include as Orthogonal Frequency Division Multiple Access (OFDMA)
205(1), Code Division Multiple Access (CDMA) sub-channel 205(2),
Time Division Multiple Access (TDMA), and Frequency Division
Multiple Access (FDMA), and the like. Schemes for multiple-access
are known in the art and in the interest of clarity only those
aspects of multiple-access schemes 205 that are relevant to the
present invention will be discussed further herein.
[0050] The architecture 200 of joint scheduling may support
underlying a plurality of physical layer forms 210, such as
Multiple-input Multi-output (MIMO) 210(1), pre-coding 210(2),
network coding 210(3), beam-forming 210(4), transmitted diversity,
space-time coding, and the like. Techniques for physical layer
forms are known in the art and in the interest of clarity only
those aspects of physical layer forms 210 that are relevant to the
present invention will be discussed further herein.
[0051] For different multiple access schemes of the plurality of
multiple-access schemes 205 and the plurality of physical layer
forms 210, an optimization of a system performance metric may be
based on degree of information available for optimization such as
knowledge or feedback of a radio channel condition. In particular,
the joint virtual scheduler 108 may use feedback 215 including, but
not limited to, a signal quality measure of a received (RX) signal
215(1), a channel (CH) characteristic 215(2) and a channel
predicate 215(3) of a distributed joint virtual scheduling. To
provide inter-cell and intra-cell transmission (TX) control 220,
the architecture 200 of joint scheduling may support a TX schedule
220(1), a TX power 220(2), and a TX bandwidth 220(3).
[0052] In partitioning of the set of virtual channels 145 by time,
frequency, space, antenna, and/or codes for the cluster 110a of
cells, the combination of these variables for the virtual channel
may be based on the use of the physical layer form 210 and the
multiple-access scheme 205. The resource partition for the virtual
channel should be dynamic in real time to adapt to the channel
variation of each user and the user mobility.
[0053] According to one embodiment of the joint virtual scheduler
108, the joint virtual scheduler 108 may support soft-handover for
a HSDPA system. In the HSDPA system, one of the primary
interference sources is the inter-cell interference. For example, a
significant inter-cell interference is observed at a region where
the associated dedicated channels (DCHs) are in soft-handover. If
soft-handover is supported for the HSDPA users, the sources of the
inter-cell interference for each user result in the signal
enhancement when the users are in a handover region. When the
soft-handover is supported for the HSDPA users, the virtual channel
comprises the HSDPA physical channels from all the cells 110
involved in the handover and has the macro diversity gain in the
received signals. Since the inter-cell interference mitigates to,
in turn, provide the signal enhancement, as the joint virtual
scheduler 108 brings the interference under control, it may support
the HSDPA soft handover for the HSDPA users.
[0054] Another embodiment of the joint virtual scheduler 108 may
support macro-diversity coherent combining in the OFDMA air
interface. In the OFDMA system, one of the primary interference
sources is the co-channel interference from the neighboring cell
110(m), as shown in FIG. 1. For a universal reuse, in the OFDMA
system, the mutual interferences are generated at an overlap region
covered by multiple cells 110 when the contents in each sub-channel
are different from different cells 110 and are scheduled for
transmission independently. A macro-diversity scheme may schedule
the same set of data transmission of the sub-channels from all
cells in the overlap region for a specific user. Since the virtual
channel of the OFDMA system with the macro-diversity scheme
provides an orthogonal set at the overlap region, the interference
may mitigate as the signal enhancement. For joint scheduling in the
OFDMA system, the joint virtual scheduler 108 may coordinate the
sub-channel joint assignments for all the cells in the cluster
110a.
[0055] FIG. 3 depicts a stylized representation for implementing a
method of coordinating a joint scheduling of the transmissions
130(1, 2), 135(1), and 135(2) based on power assignments in the
UMTS Long Term Evolution system 100 shown in FIG. 1 consistent with
an exemplary embodiment of the present invention. At block 300, the
joint virtual scheduler 108 may use the set of virtual channels 145
for active users and the signaling messages (SIG_MSG) 150(1, 2)
between the base stations 105(1, 2) for jointly scheduling the
inter-cell transmission 135(2) with intra-cell transmissions 130(1,
2) and 135(1) for the cluster 110a of cells. To enable the
intra-cell transmissions 130(1, 2) and 135(1) orthogonal within the
cluster 110a of cells of the plurality of cells 110(1-m) and the
inter-cell transmission 135(2) orthogonal across the cluster 110a
of cells associated with the base stations 105(1, 2), the joint
virtual scheduler 108 may provide the set of virtual channels 145
to assign a virtual channel to each user in the cluster 110a of
cells.
[0056] By exchanging the signaling messages (SIG_MSG) 150(1, 2)
between the base stations 105(1, 2), at block 305, the joint
virtual scheduler 108 may coordinate scheduling of the inter-cell
transmission 135(2) with intra-cell transmissions 130(1, 2) and
135(1) for the cluster 110a of cells. The joint virtual scheduler
108 may coordinate control and virtual channel assignment between
the cluster 110a of cells to manage overall interference for the
cluster 110a of cells. Using the parameter optimization algorithm
140, the joint virtual scheduler 108 may determine power
assignments of optimal power levels for the active users and
communicate to the first and second base stations 105(1, 2),
respectively. Based on the optimal power levels, which maximizes
the system throughput/capacity of the UMTS Long Term Evolution
system 100, the joint virtual scheduler 108 may jointly schedule
the Access Terminals 120(1, 2) and 125(1) of the active users
within the cluster 110a of cells, as indicated in block 310.
[0057] Consistent with one embodiment of the present invention, the
joint virtual scheduler 108 may be an aggressive interference
management scheme that coordinates control and assignment between
the cluster 110a of cells. The joint virtual scheduler 108 may rely
on the high-speed data link 170(1) for optimal performance between
processing nodes, i.e., the cells 110 or associated processors of
the base stations 105 for providing relatively fast communications
between the cells 110 to enable the UMTS Long Term Evolution system
100 to fetch the information of the radio channel characteristics
for each user and the cross correlation between the cells 110 for
interference management. For providing the interference management,
the joint virtual scheduler 108 may deliver control information,
such as a precise time stamp to each base station 105. This
information exchange may occur over the high-speed data link 170(1)
between processing nodes, which may include the base stations 105,
the controllers, and/or the processors.
[0058] However, the conventional UMTS system Specifications specify
a U-plane UMTS Terrestrial Radio Access Network (UTRAN) delay
requirement of 5 ms in an unload condition. This U-plane delay is
defined in terms of the one-way transit time between a packet being
available at the Internet Protocol (IP) layer in either the User
Equipment (UE), such as the AT 120/Radio Access Network (RAN) edge
node and the availability of this packet at the IP layer in the RAN
edge node/UE, i.e., the AT 120. This RAN edge node is a node that
provides an RAN interface towards a core network (CN).
[0059] Specifications of the UMTS Long Term Evolution system 100
may enable an Evolved UTRAN (E-UTRAN) U-plane latency of less than
5 ms in the unload condition (i.e., a single user with a single
data stream) for small a IP packet, e.g., a 0 byte payload+IP
headers in a E-UTRAN bandwidth mode may impact an experienced
latency. This U-Plane latency may indicate a desire for a
high-speed inter-connection between the processing nodes, such as
the base stations 105 within the UTRAN. In the conventional UMTS
system, however, an IP transmission over T1/E1/J1 in the UTRAN may
not meet a UTRAN latency threshold. To meet the delay thresholds, a
10 BaseT Ethernet, 100 BaseT Ethernet, gigabit Ethernet, 10 Giga
Ethernet or 100 Giga Ethernet may provide inter-connection between
the processing nodes including the base stations 105. For example,
the gigabit Ethernet with high capacity to support such
inter-connection uses gigabit Ethernet switches or hops, which may
support a QoS feature to control the latency in the UMTS Long Term
Evolution system 100. By using the gigabit Ethernet as the UTRAN
transport, the UMTS Long Term Evolution system 100 may configure
the gigabit Ethernet switch for exchanging the control information
and interference management information between the processing
nodes including the base stations 105 with a relatively high QoS
priority to minimize their latency.
[0060] The desired U-Plane Delay latency also indicates use of a
high-speed data processing capability for a data chain in the
UTRAN. The high-speed data links 170(1) between the processing
nodes including the base stations 105 may enable distributed
processing capabilities for the joint virtual scheduler 108. For
example, high-speed computational processors may be used in one
embodiment for enabling the distributed processing capabilities.
Such a distributed processing may not only be beneficial in
colleting information and computation for the interference
management in the joint virtual scheduler 108, but may reduce the
overall costs.
[0061] In one illustrative embodiment, to coordinate the radio
resource in the UMTS Long Term Evolution system 100 and manage the
overall system interference for all the cells in the cluster 110a,
the joint virtual scheduler 108 may use a common reference time
among all cells in the cluster 110a. While this common reference
time among all cells in the cluster 110a may provide a reference of
all control information and interference management, the
conventional UMTS system deploys a free running clock with a
desired high accuracy in the base stations 105 without a
synchronization therebetween. Although, a common network clock for
a hierarchical network in the UTRAN and the core network is
available, such a network clock may not meet a desired accuracy.
Accordingly, in the UMTS Long Term Evolution system 100, may use
system and frame counters, such as System Frame Number (SFN), Node
B Frame Number (BFN), RNC common Frame Number (RFN), and Cell
System Frame Number (CFN) to provide a data link and virtual
synchronization between the base stations 105.
[0062] Alternatively, in the W-CDMA system, where interference is
managed through non-coordinated power control, use of a free
running clock along with inaccurate network synchronization may
manipulate the cross-interference. Use of the reference time for
other multiple access technologies, such as OFDMA and TDMA with
stringent synchronization between the processing nodes including
the base stations 105 enables the interference management, such as
interference avoidance and coordination.
[0063] In another embodiment, the Global Positioning System (GPS)
time may be used to provide a common reference time since each cell
in the cluster 110a may independently measure with substantially
the same accuracy. For example, the GPS time is used by the CDMA
system to synchronize the base stations 105 and support the
handover. Likewise, the GPS absolute time may provide a common
reference time for the joint virtual scheduler 108 to control the
system information, to manage the interference, and to schedule the
virtual channel for each cell 110.
[0064] In one embodiment, the architecture 200 shown in FIG. 2 may
be consistent with a base station router (BSR) while coupling the
base stations 105 (1, 2) in the cluster 110a with the high-speed
communication links 170 and using the joint virtual scheduler 108
to interconnect all the base stations 105 in a distributed manner.
A distributed architecture with a virtual controller based on the
BSR may comprise a virtual scheduler server that may be a
distributed computational node that collects feedback information
and user information from each base station 105 and assigns virtual
channels to all users in the cluster 110a to maximize the system
performance. The virtual scheduler server may be distributed at
each base station 105 such that a base station provides a primary
node for the information distribution, parallel computation, and
information collection for final scheduling and virtual channel
assignment. The distributed virtual scheduler server architecture
may enhance some of the HSDPA/E-DCH features for the high-speed
communication links 170 between the base stations 105 for
coordination and management.
[0065] Another alternative of the distributed virtual scheduler
server architecture is a dedicated scheduling server for enabling a
joint scheduling control in which all base stations 105 operate as
a client to the dedicated scheduling server. The dedicated
scheduler server based client-server architecture may enable an
efficient joint virtual channel assignment and overall resource
management while effective in cost control.
[0066] The feedback and user information used by the joint virtual
scheduler 108 may include the radio channel conditions of each
user, buffer data and its time stamp for each user, user mobility,
and user capability information. To minimize the interference while
maximizing the system throughput/capacity, the joint virtual
scheduler 108 may collect the feedback and user information from
all cells 110 in the cluster 110a as an input and then perform a
virtual channel assignment for each user in the cluster 110a based
on the feedback and user information.
[0067] For optimizing a parameter associated with scheduling of a
plurality of users from the cluster 110a of cells, in the UMTS Long
Term Evolution system 100, the joint virtual scheduler 108 may
search an optimal power level for the parameter of each user of the
plurality of users. A search algorithm may maximize an indication
of system capacity of the UMTS Long Term Evolution system 100 by
jointly scheduling the plurality of users active in the cluster
110a of cells based on the optimal power levels. For example, the
joint virtual scheduler 108 may use the parameter optimization
algorithm 140 to search for a sub-optimal solution of a resource
for each user in the cluster 110a of cells. In this way, the joint
virtual scheduler 108 may schedule each user in the cluster 110a of
cells based on an optimization of power level as an objective
function being the sum of the Shannon capacity of the plurality of
users in the cluster 110a of cells.
[0068] The joint virtual scheduler 108 may be based on a virtual
channel structure model for N users in the UMTS Long Term Evolution
system 100 (in whole clusters) in which a matrix A comprises
matrices of the correlation between the base stations 105, the
physical layer forms 210 shown in FIG. 2 for the N users in the
cluster 110a. Each correlation matrix indicates a joint channel
correlation in space, time, frequency, code, antenna technology,
and coding technology. A vector x indicates the desired virtual
channels for all N users in the joint virtual scheduler 108. The
vector x may be a function of space, time, frequency, code, antenna
technology, and coding technology in the following,
x .fwdarw. = [ x 1 x 2 x N ] and x i = g ( s , f , t , a , c , sf )
i = 1 , 2 , , N ##EQU00001## [0069] g: a general function [0070] s:
a set of space attenuation functions between the users and the base
stations 105 (1, 2) in the cluster 110a. S is a multi-dimensional
attenuation function relative to all the base stations 105 (1, 2)
in the cluster 110a. [0071] t: a set of transmit time slots for a
transmission among base stations in the cluster 110a [0072] f: a
set of frequency band or frequency sub-channels for a sub-carrier.
[0073] a: a set of antenna patterns and technologies, such as the
MIMO 210(1), transmit diversity, beam-forming 210(4), [0074] c: a
set of coding and pre-coding schemes [0075] sf: a set of the time
domain spreading codes for a spread spectrum communication.
[0076] According to one solution of the virtual channel assignment,
the vector x is the Eign vector of the correlation matrix A. In
this solution, the Eign value of the matrix A indicates the energy
distribution on each Eign vector. However, the matrix A is a
function of multiple variables, such as the attenuation relative to
each base station, channel correlation between antenna in each base
station, the frequency selectivity effect of sub-channel, the
spreading sequence and the channel correlation between the time
slots. Each variable increases the dimension of the matrix A
multiple times depending upon the basis of that variable. Multiple
variables cause a multiplicity of effects on a single variable. The
complexity and the dimensions of the matrix A increase multi-fold
when all the supported physical layer forms 210 and the
multiple-access schemes 205 are considered for all base stations
105 in the clusters 110a.
[0077] Accordingly, to obtain a desired solution, the complicity of
the matrix A may be reduced by simplifying the generic correlation
matrix A as the physical layer forms 210 or defining a specific
multiple-access scheme 205. For example, in a generic R-99 single
antenna W-CDMA DL system, as the time, frequency, code, and antenna
are constants, the spreading codes are an orthogonal set within
same scrambling code. Moreover, the matrix A is a function of space
and the cross correlation between the scrambling code between the
base stations 105. Thus, the joint virtual scheduler 108 provides a
scrambling set for all the base stations 105 to minimize the cross
interference for all users in the clusters 110a.
[0078] However, if a single antenna HSDPA system is indicated for
the matrix A, the joint virtual scheduler 108 includes the time
variable to provide a scrambling code set that minimizes the
cross-interference for the user scheduled at that time. Since the
HSDPA system supports multi-user scheduling in a TTI, instead of
using a new scrambling code set to minimize the cross-interference
for obtaining a sub-optimal solution, alternatively the joint
virtual scheduler 108 may manage the interference with the current
scramble code set. This solution of the interference management in
the HSDPA system may support the soft-handover for all users in a
handover region. When users are in the handover region, the joint
virtual scheduler 108 may coordinate the transmission time with the
same set of HS-PDSCH codes among all base stations 105
participating in the soft handover. The joint virtual scheduler 108
may minimize the cross or inter-cell interference since the
interference source has been mitigated into a signal enhancement.
As a result, the HSDPA users may receive a macro-diversity gain
through this soft handover support.
[0079] Likewise, for a OFDMA system since the variables of the
matrix A consist of frequency, time, and space, the joint virtual
scheduler 108 may incorporate the overall sub-channel assignments
jointly to the users of all base stations 105 in the cluster 110a
in a given time slots to minimize the overall interference. In the
OFDMA system, the interference management mitigates the co-channel
interference into the signal enhancement. Moreover, the joint
virtual scheduler 108 may achieve a target of the universal reuse
by tightly coordinating the transmission and sub-channel
assignments for the cell 110(2) and its neighboring cells, such as
the cell 110(m).
[0080] To provide joint sub-channel assignments with a given
maximum gain, the joint virtual scheduler 108 may assign the
channel to the users of the maximum combining gain and minimum
co-channel interference. While, such a simplified matrix A
indicates the correlation of sub-channel sets for each base station
105 relative to each user, the sub-channel assignment and
co-channel interference may be characterized by the spatial
attenuation from each base station to all users. The joint virtual
scheduler 108 may partition all sub-channels for all cells 110 in
the cluster 110a and indicate a scheduling strategy for the
sub-channel assignment to each user. In this way, the joint virtual
scheduler 108 may coordinate transmission scheduling in the OFDMA
system with maximum system performance.
[0081] To provide a scheduling strategy for a coordinated joint
scheduling in an OFDMA system, the joint virtual scheduler 108 may
schedule power, e.g., in time and frequency domains, for the
transmissions from all base stations 105 in a cluster 110a to all
UEs, i.e., the ATs 120, 125 in this cluster. The power is assigned
in such a way that it maximizes the total throughput subject to a
power constraint for each base station 105. The joint virtual
scheduler 108 may use Shannon capacity to represent throughput,
which implicitly implies that the data rates for the ATs 120, 125
may be selected accordingly.
[0082] In a frequency domain scheduling at any given time, the
joint virtual scheduler 108 may maximize the total
throughput/capacity. By adding scheduling in time domain, the joint
virtual scheduler 108 may solve a functional optimization problem.
By focusing on a given time first, i.e., frequency domain
scheduling, the joint virtual scheduler 108 may provide a
parametric optimization, as defined below: [0083] g.sub.i,j,k=link
gain (in power) from a base station (BS) i to User Equipment (UE)
or AT k on a channel j. The link gain indicates the correlation
function for each user relative to each channel of every base
station in the matrix A. [0084] P.sub.i,j,k=transmit power from BS
i to UE k on a channel j [0085] where, [0086] i.epsilon.{1, . . .
,I}, I is the total number of base stations 105 in the cluster 110a
[0087] j.epsilon.{1, . . . ,J}, J is the number of sub-channels in
each base station 105 that may be assigned to the UEs [0088]
k.epsilon.{1, . . . ,K}, K is the total number of UEs in the
cluster 110a
[0089] Following shows a problem formulation:
max P _ = { p i , j , k } , .A-inverted. i .di-elect cons. { 1 , I
} , j .di-elect cons. { 1 , , J } k .di-elect cons. { 1 , , K } C
total = k = 1 K C k ( 1 ) ##EQU00002##
subject to the maximum power constraint of each base station 105 in
the following
j = 1 J k = 1 K p i , j , k .ltoreq. p 0 , .A-inverted. i .di-elect
cons. { 1 , , I } ( 2 ) where C k = j = 1 J C j , k = j = 1 J W log
2 ( 1 + S j , k I j , k C + I j , k I + .sigma. 2 ) ( 3 )
##EQU00003##
is the per UE capacity.
S j , k = i = 1 I g i , j , k p i , j , k ( 4 ) ##EQU00004##
is the signal power for UE k on channel j.
I j , k C = i = 1 I k ' = 1 , k ' .noteq. k K g i , j , k ' p i , j
, k ' ( 5 ) ##EQU00005##
is the co-channel interference caused by UE k on channel j to all
other users on that channel j
I j , k I = i = 1 I j ' = 1 j ' .noteq. j J k ' = 1 k ' .noteq. k K
g i , j ' , k ' p i , j ' k ' F j , j ' ( 6 ) ##EQU00006##
is the Inter-channel interference caused by UE k on channel j to
all other users that are channels other than j [0090] C.sub.total
is the total capacity of the cluster 110a where C.sub.k is the
capacity for the kth UE. [0091] W is the bandwidth, assumed to be
known. [0092] p.sub.0 is the maximum transmit power from a base
station 105, which is assumed to be the same for all base stations
and assumed to be known. [0093] F.sub.j,j' is the inter-channel
attenuation between channel j and channel j'. It is used to model
inter-channel interference and is assumed to be known. If a given
base transceiver station (BTS) only transmits to one UE on a given
channel, i.e., in the set of {P.sub.i,j,k}, k=1, . . . ,K, there is
at most one non-zero element for any given pair of {i,j}.
[0094] The above formulated parametric optimization problem may be
solved by classical methods such as Largrange multiplier method.
However, being a large scale system in that the dimension is large,
a central controller may optimize the total throughput by choosing
I.times.J.times.K variables. Furthermore, in this case, the
transmit power in each base station 105 may depend upon many local
constraints. To address the central optimization vs. local
constraints issue, the joint virtual scheduler 108 may use
hierarchical control and to handle the large dimension by the
central controller it may use an iteration method.
[0095] According to one embodiment of the present invention, FIG. 4
illustrates a stylized representation for implementing a method of
scheduling power in frequency domain for the transmissions 130(1,
2), 135(1), and 135(2) from the base stations 105(1, 2) to the
active Access Terminals 120(1, 2) and 125(1) in the cluster 110a of
cells to maximize the total throughput or capacity for each base
station 105 shown in FIG. 1. To this end, the parameter
optimization algorithm 140 may comprise a High layer (HL) algorithm
portion and a Lower layer (LL) algorithm portion, as shown in FIG.
4. As can be seen, the HL algorithm portion receives .lamda..sub.i,
i=1, . . . ,N, the power penalty from the LL algorithm portion. The
HL algorithm portion allocates power in a small amount .DELTA.p by
.DELTA.p. For each {i,j,k}, there are three associated quantities:
[0096] 1. Throughput gain A.sub.i,j,k(P)--gain in throughput for
self if .DELTA.p is allocated to {i,j,k}, given the current power
allocation P [0097] 2. Co-channel and inter-channel interference
penalty B.sub.i,j,k(P)--penalty (loss in other user's throughput)
if .DELTA.p is allocated to {i,j,k}, given the current power
allocation P [0098] 3. Base station power penalty .lamda..sub.i,
the power penalty from the LL algorithm portion.
[0099] In the HL algorithm portion, the power calculation is set
forth in the following where the values of A.sub.i,j,k, B.sub.i,j,k
may be calculated using partial directives evaluated for a given
power allocation. For example, as shown in the HL algorithm portion
below: [0100] Begin HL_Algorithm [0101] Step 1: use known link
gains {g.sub.i,j,k} and previous power allocation at iteration n:
{p.sub.i,j,k}; [0102] Step 2: Calculate S.sub.j,k, I.sub.j,k.sup.C
and I.sub.j,k.sup.I, for all j, k, using equation (4), (5) and (6)
[0103] Step 3: Calculate A.sub.i,j,k and B.sub.i,j,k for all i, j,
k. Here,
[0103] A i , j , k = .differential. C j , k .differential. p i , j
, k = W 1 + S j , k I j , k C + I j , k I + .sigma. 2 g i , j , k (
6 ) ##EQU00007## [0104] Similarly, the HL_algorithm determines
B.sub.i,j,k as well for all possible {i,j,k}. [0105] Step 4:
calculate the TX credit for all i,j,k:
[0105] L.sub.i,j,k=A.sub.i,j,k-B.sub.i,j,k-.lamda..sub.i (8) [0106]
Step 5: ordering L.sub.i,j,k and if L.sub.i,j,k>0,
p.sub.i,j,k=p.sub.i,j,k+.DELTA. [0107] Step 6: repeat until max
L.sub.i,j,k<0 [0108] End of HL_algorithm.
[0109] In Step 7, for each base station 105, the LL algorithm
portion updates and provides .lamda..sub.i, i=1 . . . ,N, the power
penalty to the HL algorithm portion. Finally, at step 8, the LL
algorithm portion determines the power assignments for each base
station {P i,j,k}. However, to schedule power in time domain, the
parameter optimization algorithm 140 may perform additional steps,
as described below.
[0110] In accordance with one illustrative embodiment of the
present invention, FIG. 5 illustrates a stylized representation for
implementing a method of scheduling power in time domain for the
transmissions 130(1, 2), 135(1), and 135(2) from the base stations
105(1, 2) to the active Access Terminals 120(1, 2) and 125(1) in
the cluster 110a of cells to maximize the total throughput or
capacity for each base station shown in FIG. 1. While in block 500,
the maximization problem indicated above in FIG. 4 may be modified
by adding a credit/penalty for "fairness." At block 505, the
fairness may be maintained.
[0111] Table 1 below compares some metrics including priority
ordering, credit and penalty of a conventional scheduling
algorithm, such as a Proportional Fair (PF) scheduler, with the
joint virtual scheduler 108.
TABLE-US-00001 Current scheduler Joint Scheduler Priority ordering
within ordering for a pool of BTSs ordering each BTS and
sub-channels Credit Self-throughput (C/I) Self-throughput Fairness
penalty (in time) Fairness penalty (in time) Co-channel and
inter-channel interference to others Penalty TX power impact on
specific BTS total power
[0112] In one embodiment, the high-speed wireless access network
115 may wirelessly communicate mobile data at a speed and coverage
desired by individual users or enterprises. According to one
embodiment, the high-speed wireless data network 120 may comprise
one or more data networks, such as Internet Protocol (IP) network
comprising the Internet and a public telephone system (PSTN). The
3rd generation (3G) mobile communication system, namely Universal
Mobile Telecommunication System (UMTS) supports multimedia services
according to 3rd Generation Partnership Project (3GPP)
specifications. The UMTS adapts the Wideband Code Division Multiple
Access (WCDMA) technology and includes Core Networks (CN) that are
packet switched networks, e.g., IP-based networks. Because of the
merging of Internet and mobile applications, the UMTS users can
access both telecommunications and Internet resources. To provide
an end-to-end service to users, a UMTS network may deploy a UMTS
bearer service layered architecture specified by Third Generation
Project Partnership (3GPP) standard. The provision of the
end-to-end service is conveyed over several networks and realized
by the interaction of the protocol layers.
[0113] Portions of the present invention and corresponding detailed
description are presented in terms of software, or algorithms and
symbolic representations of operations on data bits within a
computer memory. These descriptions and representations are the
ones by which those of ordinary skill in the art effectively convey
the substance of their work to others of ordinary skill in the art.
An algorithm, as the term is used here, and as it is used
generally, is conceived to be a self-consistent sequence of steps
leading to a desired result. The steps are those requiring physical
manipulations of physical quantities. Usually, though not
necessarily, these quantities take the form of optical, electrical,
or magnetic signals capable of being stored, transferred, combined,
compared, and otherwise manipulated. It has proven convenient at
times, principally for reasons of common usage, to refer to these
signals as bits, values, elements, symbols, characters, terms,
numbers, or the like.
[0114] It should be borne in mind, however, that all of these and
similar terms are to be associated with the appropriate physical
quantities and are merely convenient labels applied to these
quantities. Unless specifically stated otherwise, or as is apparent
from the discussion, terms such as "processing" or "computing" or
"calculating" or "determining" or "displaying" or the like, refer
to the action and processes of a computer system, or similar
electronic computing device, that manipulates and transforms data
represented as physical, electronic quantities within the computer
system's registers and memories into other data similarly
represented as physical quantities within the computer system
memories or registers or other such information storage,
transmission or display devices.
[0115] Note also that the software implemented aspects of the
invention are typically encoded on some form of program storage
medium or implemented over some type of transmission medium. The
program storage medium may be magnetic (e.g., a floppy disk or a
hard drive) or optical (e.g., a compact disk read only memory, or
"CD ROM"), and may be read only or random access. Similarly, the
transmission medium may be twisted wire pairs, coaxial cable,
optical fiber, or some other suitable transmission medium known to
the art. The invention is not limited by these aspects of any given
implementation.
[0116] The present invention set forth above is described with
reference to the attached figures. Various structures, systems and
devices are schematically depicted in the drawings for purposes of
explanation only and so as to not obscure the present invention
with details that are well known to those skilled in the art.
Nevertheless, the attached drawings are included to describe and
explain illustrative examples of the present invention. The words
and phrases used herein should be understood and interpreted to
have a meaning consistent with the understanding of those words and
phrases by those skilled in the relevant art. No special definition
of a term or phrase, i.e., a definition that is different from the
ordinary and customary meaning as understood by those skilled in
the art, is intended to be implied by consistent usage of the term
or phrase herein. To the extent that a term or phrase is intended
to have a special meaning, i.e., a meaning other than that
understood by skilled artisans, such a special definition will be
expressly set forth in the specification in a definitional manner
that directly and unequivocally provides the special definition for
the term or phrase.
[0117] While the invention has been illustrated herein as being
useful in a telecommunications network environment, it also has
application in other connected environments. For example, two or
more of the devices described above may be coupled together via
device-to-device connections, such as by hard cabling, radio
frequency signals (e.g., 802.11(a), 802.11(b), 802.11(g), 802.16,
Bluetooth, or the like), infrared coupling, telephone lines and
modems, or the like. The present invention may have application in
any environment where two or more users are interconnected and
capable of communicating with one another.
[0118] Those skilled in the art will appreciate that the various
system layers, routines, or modules illustrated in the various
embodiments herein may be executable control units. The control
units may include a microprocessor, a microcontroller, a digital
signal processor, a processor card (including one or more
microprocessors or controllers), or other control or computing
devices as well as executable instructions contained within one or
more storage devices. The storage devices may include one or more
machine-readable storage media for storing data and instructions.
The storage media may include different forms of memory including
semiconductor memory devices such as dynamic or static random
access memories (DRAMs or SRAMs), erasable and programmable
read-only memories (EPROMs), electrically erasable and programmable
read-only memories (EEPROMs) and flash memories; magnetic disks
such as fixed, floppy, removable disks; other magnetic media
including tape; and optical media such as compact disks (CDs) or
digital video disks (DVDs). Instructions that make up the various
software layers, routines, or modules in the various systems may be
stored in respective storage devices. The instructions, when
executed by a respective control unit, causes the corresponding
system to perform programmed acts.
[0119] The particular embodiments disclosed above are illustrative
only, as the invention may be modified and practiced in different
but equivalent manners apparent to those skilled in the art having
the benefit of the teachings herein. Furthermore, no limitations
are intended to the details of construction or design herein shown,
other than as described in the claims below. It is therefore
evident that the particular embodiments disclosed above may be
altered or modified and all such variations are considered within
the scope and spirit of the invention. Accordingly, the protection
sought herein is as set forth in the claims below.
* * * * *