U.S. patent application number 17/566037 was filed with the patent office on 2022-04-21 for methods and apparatuses for reference signal allocation.
This patent application is currently assigned to NEC CORPORATION. The applicant listed for this patent is NEC CORPORATION. Invention is credited to Yukai GAO, Gang WANG.
Application Number | 20220123914 17/566037 |
Document ID | / |
Family ID | 1000006066312 |
Filed Date | 2022-04-21 |
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United States Patent
Application |
20220123914 |
Kind Code |
A1 |
GAO; Yukai ; et al. |
April 21, 2022 |
METHODS AND APPARATUSES FOR REFERENCE SIGNAL ALLOCATION
Abstract
Embodiments of the present disclosure relate to methods and
devices for reference signal allocation. In example embodiments, a
method implemented in a network device is provided. According to
the method, a plurality of RS configurations are determined based
on at least one of the following: different RS ports, or different
RS sequences of a same type. At least one first RS configuration
from the plurality of RS configurations are allocated for uplink RS
transmission by a terminal device served by the network device, and
at least one second RS configuration from the plurality of RS
configurations are allocated for downlink RS transmission by the
network device.
Inventors: |
GAO; Yukai; (Beijing,
CN) ; WANG; Gang; (Beijing, CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NEC CORPORATION |
Tokyo |
|
JP |
|
|
Assignee: |
NEC CORPORATION
Tokyo
JP
|
Family ID: |
1000006066312 |
Appl. No.: |
17/566037 |
Filed: |
December 30, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
16486106 |
Aug 14, 2019 |
11258574 |
|
|
PCT/CN2017/079083 |
Mar 31, 2017 |
|
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17566037 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04B 7/0626 20130101;
H04L 25/0226 20130101; H04L 5/10 20130101; H04L 5/0051
20130101 |
International
Class: |
H04L 5/10 20060101
H04L005/10; H04B 7/06 20060101 H04B007/06; H04L 5/00 20060101
H04L005/00; H04L 25/02 20060101 H04L025/02 |
Claims
1. A terminal comprising a processor configured to: receive, from a
network device, a parameter; receive, from the network device,
information on a DMRS configuration indicating DMRS port(s) and
DMRS sequence(s) for a DMRS transmission; and perform the DMRS
transmission between the terminal and the network device based on
the DMRS configuration, wherein DMRS configurations are divided
into groups, a group from the groups is identified by the
parameter, the information indicates the DMRS configuration
belonging to the group identified by the parameter, and two
different DMRS sequences are used for a same DMRS port for two
different DMRS configurations within the group.
2. The terminal according to claim 1, wherein two different DMRS
sequences are generated based on different initial values.
3. The terminal according to claim 1, wherein the DMRS
configurations are based on a maximum number of DMRS ports.
4. A network device comprising a processor configured to: transmit,
to a terminal, a parameter; transmit, to the terminal, information
on a DMRS configuration indicating DMRS port(s) and DMRS
sequence(s) for a DMRS transmission; and perform the DMRS
transmission between the terminal and the network device based on
the DMRS configuration, wherein DMRS configurations are divided
into groups, a group from the groups is identified by the
parameter, the information indicates the DMRS configuration
belonging to the group identified by the parameter, and two
different DMRS sequences are used for a same DMRS port for two
different DMRS configurations within the group.
5. The network device according to claim 4, wherein two different
DMRS sequences are generated based on different initial values.
6. The network device according to claim 4, wherein the DMRS
configurations are based on a maximum number of DMRS ports.
7. A method comprising: receiving a parameter; receiving
information on a DMRS configuration indicating DMRS port(s) and
DMRS sequence(s) for a DMRS transmission; and performing the DMRS
transmission based on the DMRS configuration, wherein DMRS
configurations are divided into groups, a group from the groups is
identified by the parameter, the information indicates the DMRS
configuration belonging to the group identified by the parameter,
and two different DMRS sequences are used for a same DMRS port for
two different DMRS configurations within the group.
8. The method according to claim 7, wherein two different DMRS
sequences are generated based on different initial values.
9. The method according to claim 7, wherein the DMRS configurations
are based on a maximum number of DMRS ports.
10. A method comprising: transmitting a parameter; transmitting
information on a DMRS configuration indicating DMRS port(s) and
DMRS sequence(s) for a DMRS transmission; and performing the DMRS
transmission based on the DMRS configuration, wherein DMRS
configurations are divided into groups, a group from the groups is
identified by the parameter, the information indicates the DMRS
configuration belonging to the group identified by the parameter,
and two different DMRS sequences are used for a same DMRS port for
two different DMRS configurations within the group.
11. The method according to claim 10, wherein two different DMRS
sequences are generated based on different initial values.
12. The method according to claim 10, wherein the DMRS
configurations are based on a maximum number of DMRS ports.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a Continuation of U.S. application Ser.
No. 16/486,106, filed Aug. 14, 2019, which is a 371 national stage
application of International Application No. PCT/CN2017/079083,
filed Mar. 31, 2017, the disclosures of all of which are
incorporated herein in their entirety.
TECHNICAL FIELD
[0002] Embodiments of the present disclosure generally relate to
the field of telecommunication, and in particular, to methods and
apparatuses for reference signal (RS) allocation in uplink and
downlink.
BACKGROUND
[0003] With the development of communication technologies, multiple
types of services or traffic have been proposed, for example,
enhanced mobile broadband (eMBB) generally requiring high data
rate, massive machine type communication (mMTC) typically requiring
long battery lifetime, and ultra-reliable and low latency
communication (URLLC). Meanwhile, multi-antenna schemes, such as
beam management, reference signal transmission, and so on, are
studied for new radio access.
[0004] Conventionally, a network device (for example, an eNB)
transmits downlink reference signals (RSs) such as Demodulation
Reference Signal (DMRS), Channel State Information-Reference Signal
(CSI-RS), Sounding Reference Signal (SRS), and the like. A terminal
device, such as user equipment (UE) in the system may receive the
downlink reference signals on allocated resources, including for
example, one or more resource elements (REs). The terminal device
may also transmit uplink reference signals to the network device on
corresponding allocated resources. The downlink and uplink
reference signals may be used for channel estimation, demodulation,
and the like at the receiving terminal device and network device
sides.
[0005] As increasing of the number of available antenna ports and
development of the communication technologies, new requirements are
imposed on downlink and uplink transmission of reference signals,
for example, structures designed for the downlink and uplink
reference signals, sequences used in downlink and uplink reference
signals, resource allocated for the downlink and uplink reference
signals, and the like.
SUMMARY
[0006] In general, example embodiments of the present disclosure
provide methods and apparatuses for reference signal (RS)
allocation in uplink and downlink.
[0007] In a first aspect, there is provided a method implemented in
a network device. According to the method, a plurality of RS
configurations are determined based on at least one of the
following: different RS ports, or different RS sequences of a same
type. At least one first RS configuration from the plurality of RS
configurations are allocated for uplink RS transmission by a
terminal device served by the network device, and at least one
second RS configuration from the plurality of RS configurations are
allocated for downlink RS transmission by the network device.
[0008] In a second aspect, there is provided a method implemented
in a terminal device. According to the method, information on at
least one first RS configuration among a plurality of RS
configurations is received from a network device. The plurality of
RS configurations being determined based on at least one of the
following: different RS ports, or different RS sequences of a same
type, and at least one second RS configuration among the plurality
of RS configurations being allocated for downlink RS transmission
by the network device. A RS sequence is transmitted to the network
device based on the at least one first RS configuration.
[0009] In a third aspect, there is provided a network device. The
network device includes a controller configured to determine a
plurality of RS configurations based on at least one of the
following: different RS ports, or different RS sequences of a same
type; allocate at least one first RS configuration from the
plurality of RS configurations for uplink RS transmission by a
terminal device served by the network device; and allocate at least
one second RS configuration from the plurality of RS configurations
for downlink RS transmission by the network device.
[0010] In a fourth aspect, there is provided a terminal device. The
terminal device includes a receiver configured to receive from a
network device information on at least one first RS configuration
among a plurality of RS configurations, the plurality of RS
configurations being determined based on at least one of the
following: different RS ports, or different RS sequences of a same
type, and at least one second RS configuration among the plurality
of RS configurations being allocated for downlink RS transmission
by the network device. The terminal device also includes a
transmitter configured to transmit a RS sequence to the network
device based on the at least one first RS configuration.
[0011] In a fifth aspect, there is provided a device. The apparatus
includes a processor; and a memory coupled to the processing unit
and storing instructions thereon, the instructions, when executed
by the processing unit, causing the apparatus to perform the method
according to the first aspect.
[0012] In a sixth aspect, there is provided a device. The apparatus
includes a processor; and a memory coupled to the processing unit
and storing instructions thereon, the instructions, when executed
by the processing unit, causing the apparatus to perform the method
according to the second aspect.
[0013] Other features of the present disclosure will become easily
comprehensible through the following description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] Through the more detailed description of some embodiments of
the present disclosure in the accompanying drawings, the above and
other objects, features and advantages of the present disclosure
will become more apparent, wherein:
[0015] FIG. 1 is a block diagram of a communication environment in
which embodiments of the present disclosure can be implemented;
[0016] FIG. 2 is an illustrative diagram showing multiplexing of
different reference signals;
[0017] FIG. 3 is a flowchart illustrating a process for reference
signal allocation according to some embodiments of the present
disclosure;
[0018] FIGS. 4A-4F are illustrative diagrams showing group division
of RS configurations in accordance with some embodiments of the
present disclosure;
[0019] FIGS. 5A-5D show examples of multiplexing of different
reference signals according to some embodiments of the present
disclosure;
[0020] FIGS. 6A-6D show examples of extension of RS transmission
according to some embodiments of the present disclosure;
[0021] FIG. 7 shows a flowchart of an example method in accordance
with some embodiments of the present disclosure;
[0022] FIG. 8 shows a flowchart of an example method in accordance
with some other embodiments of the present disclosure;
[0023] FIG. 9 is a block diagram of a network device in accordance
with some embodiments of the present disclosure;
[0024] FIG. 10 is a block diagram of a terminal device in
accordance with some embodiments of the present disclosure; and
[0025] FIG. 11 is a simplified block diagram of a device that is
suitable for implementing embodiments of the present
disclosure.
[0026] Throughout the drawings, the same or similar reference
numerals represent the same or similar element.
DETAILED DESCRIPTION
[0027] Principle of the present disclosure will now be described
with reference to some example embodiments. It is to be understood
that these embodiments are described only for the purpose of
illustration and help those skilled in the art to understand and
implement the present disclosure, without suggesting any
limitations as to the scope of the disclosure. The disclosure
described herein can be implemented in various manners other than
the ones described below.
[0028] In the following description and claims, unless defined
otherwise, all technical and scientific terms used herein have the
same meaning as commonly understood by one of ordinary skills in
the art to which this disclosure belongs.
[0029] As used herein, the term "network device" or "base station"
(BS) refers to a device which is capable of providing or hosting a
cell or coverage where terminal devices can communicate. Examples
of a network device include, but not limited to, a Node B (NodeB or
NB), an Evolved NodeB (eNodeB or eNB), a NodeB in new radio access
(gNB) a Remote Radio Unit (RRU), a radio head (RH), a remote radio
head (RRH), a low power node such as a femto node, a pico node, and
the like. For the purpose of discussion, in the following, some
embodiments will be described with reference to eNB as examples of
the network device.
[0030] As used herein, the term "terminal device" refers to any
device having wireless or wired communication capabilities.
Examples of the terminal device include, but not limited to, user
equipment (UE), personal computers, desktops, mobile phones,
cellular phones, smart phones, personal digital assistants (PDAs),
portable computers, image capture devices such as digital cameras,
gaming devices, music storage and playback appliances, or Internet
appliances enabling wireless or wired Internet access and browsing
and the like.
[0031] As used herein, the singular forms "a", "an" and "the" are
intended to include the plural forms as well, unless the context
clearly indicates otherwise. The term "includes" and its variants
are to be read as open terms that mean "includes, but is not
limited to." The term "based on" is to be read as "based at least
in part on." The term "one embodiment" and "an embodiment" are to
be read as "at least one embodiment." The term "another embodiment"
is to be read as "at least one other embodiment." The terms
"first," "second," and the like may refer to different or same
objects. Other definitions, explicit and implicit, may be included
below.
[0032] In some examples, values, procedures, or apparatus are
referred to as "best," "lowest," "highest," "minimum," "maximum,"
or the like. It will be appreciated that such descriptions are
intended to indicate that a selection among many used functional
alternatives can be made, and such selections need not be better,
smaller, higher, or otherwise preferable to other selections.
[0033] Communication discussed in the present disclosure may
conform to any suitable standards including, but not limited to,
New Radio Access (NR), Long Term Evolution (LTE), LTE-Evolution,
LTE-Advanced (LTE-A), Wideband Code Division Multiple Access
(WCDMA), Code Division Multiple Access (CDMA) and Global System for
Mobile Communications (GSM) and the like. Furthermore, the
communications may be performed according to any generation
communication protocols either currently known or to be developed
in the future. Examples of the communication protocols include, but
not limited to, the first generation (1G), the second generation
(2G), 2.5G, 2.75G, the third generation (3G), the fourth generation
(4G), 4.5G, the fifth generation (5G) communication protocols.
[0034] FIG. 1 shows an example communication network 100 in which
embodiments of the present disclosure can be implemented. The
network 100 includes a network device 110 and three terminal
devices 120-1 and 120-3 (collectively referred to as terminal
devices 120 or individually referred to as terminal device 120)
served by the network device 110. The coverage of the network
device 110 is also called as a cell 102. It is to be understood
that the number of base stations and terminal devices is only for
the purpose of illustration without suggesting any limitations. The
network 100 may include any suitable number of base stations and
the terminal devices adapted for implementing embodiments of the
present disclosure. Although not shown, it would be appreciated
that there may be one or more neighboring cells adjacent to the
cell 102 where one or more corresponding network devices provides
service for a number of terminal device located therein.
[0035] The network device 110 may communicate with the terminal
devices 120. The communications in the network 100 may conform to
any suitable standards including, but not limited to, Long Term
Evolution (LTE), LTE-Evolution, LTE-Advanced (LTE-A), Wideband Code
Division Multiple Access (WCDMA), Code Division Multiple Access
(CDMA) and Global System for Mobile Communications (GSM) and the
like. Furthermore, the communications may be performed according to
any generation communication protocols either currently known or to
be developed in the future. Examples of the communication protocols
include, but not limited to, the first generation (1G), the second
generation (2G), 2.5G, 2.75G, the third generation (3G), the fourth
generation (4G), 4.5G, the fifth generation (5G) communication
protocols.
[0036] In addition to normal data communications, the network
device 110 may send a reference signal (RS) in a broadcast,
multi-cast, and/or unicast manners to one or more of the terminal
devices 120 in a downlink. Similarly, one or more of the terminal
devices 120 may transmit RSs to the network device 110 in an
uplink. As used herein, a "downlink" refers to a link from a
network device to a terminal device, while an "uplink" refers to a
link from the terminal device to the network device.
[0037] The RS may be used by the receiving device(s) (the network
device 110 in uplink RS transmission or the terminal devices 120 in
downlink RS transmission) for channel estimation, demodulation, and
other operations for communication. Generally speaking, a RS is a
signal sequence that is known by both the network device 110 and
the terminal devices 120. For example, a RS sequence may be
generated and transmitted by a transmitting device (the network
device 110 or the terminal device 120) based on a certain rule and
a receiving device (the terminal device 120 or the network device
110) may deduce the RS sequence based on the same rule. Examples of
reference signal may include but are not limited to Demodulation
Reference Signal (DMRS), Channel State Information-Reference Signal
(CSI-RS), Sounding Reference Signal (SRS).
[0038] In transmission of downlink and uplink reference signals,
the network device 110 may assign corresponding resources for the
transmission and/or specify which sequence is transmitted. In
Multiple-Input Multiple-Output (MU-MIMO) scenarios, both the
network device 110 and terminal device 120 are equipped with
multiple antenna ports (or antenna elements) and can transmit
specified RS sequences on a certain resource region using the
antenna ports (antenna elements). A number of RS ports are also
specified. A RS port may be referred to as a specific mapping of
part or all of a RS sequence to one or more resource elements of a
resource region allocated for RS transmission in time, frequency,
and/or code domains and thus can also be called as a virtual RS
port. Generally, different RS ports are orthogonal to each other.
In order to transmit downlink and uplink RSs, the network device
110 can allocate one or more corresponding RS ports for downlink RS
transmission and one or more other corresponding RS ports for
uplink RS transmission.
[0039] For example, it has been agreed in 3GPP specification works
that a terminal device can support up to eight RS ports and thus
can be allocated with less than or equal to eight RS ports for
uplink transmission. The network device can also transmit a RS
sequence to the terminal device with at most eight RS ports.
[0040] With the development of new communication technologies, the
number of orthogonal RS ports can be increased due to increasing of
antenna ports of network devices and terminal devices and/or use of
wide frequency bands. For example, it has been proposed to specify
more than eight orthogonal RS ports for RS transmission (especially
DMRS transmission). New requirements are thus imposed on downlink
and uplink RS transmissions. For flexible duplexing and
interference cancellation, a common RS structure is needed for
downlink and uplink, which means that the resource location, the
pattern and sequences for downlink and uplink RS transmission are
common while the orthogonality may also be satisfied. In other
words, reference signals for both downlink and uplink can be
configured to be orthogonal to each other. The increasing of
orthogonal RS ports is more suitable for Multi-User Multiple-Input
Multiple-Output (MU-MIMO) scenarios and thus it is desired that
multiplexing of different terminal devices or RS transmission in
different links can be supported with the RS ports in MU-MIMO
systems.
[0041] FIG. 2 shows a diagram for such new requirements. As shown,
RS transmission is allocated with a resource region 212 in a
resource space 210 (a time and frequency resource space in this
example). The resource region 212 may correspond to a number of
orthogonal RS ports with corresponding resource mapping. For two RS
sequence 201 and 202 (downlink and/or uplink RS sequences for one
or more terminal devices), it is desired that they can be
multiplexed (220) to the resource region 212 (via corresponding RS
ports).
[0042] However, according to current communication specifications,
downlink and uplink RSs are separately designed and cannot meet the
new requirements. For example, according to current Long Term
Evolution (LTE) specification, a downlink DMRS is generated with a
pseudorandom noise (PN) sequence and are multiplexed among multiple
antenna ports of a network device using Code Division Multiple
(CDM) and Frequency Division Multiple (FDM) techniques; while an
uplink DMRS is generated with a Zadoff-Chu (ZC) sequence and are
multiplexed among multiple antenna ports of a network device using
cyclic shift (CS), CDM, and Interleaved Frequency Division Multiple
Access (IFDMA) techniques. Therefore, downlink and uplink RS
sequences designed according to current specifications cannot be
multiplexed in the same resource region (or with a same set of RS
ports).
[0043] In accordance with embodiments of the present disclosure,
there is proposed a new solution for RS allocation. In this
solution, a plurality of RS configurations are determined by a
network device based on different RS ports and/or different RS
sequences of a same type. To enable downlink and uplink RS
transmissions, the network device may allocate a subset of the
determined RS configurations for its downlink RS transmission and
another subset of the determined RS configurations for uplink RS
transmission by a terminal device served by the network device. The
network device may thus transmit a downlink RS sequence to one or
more terminal devices based on the allocated RS configuration while
the terminal device may also transmit an uplink RS sequence based
on its allocated RS configuration. Through this solution, since RS
ports are defined as orthogonal to each other and RS sequences of
the same type are generated to be at least quasi-orthogonal to each
other, the set of RS orthogonal configurations can be obtained from
the RS ports and RS sequences. On this basis, downlink and uplink
RSs transmitted with the allocated RS configuration can share a
common structure and achieve orthogonality.
[0044] Principle and implementations of the present disclosure will
be described in detail below with reference to FIG. 3, which shows
a process 300 for reference signal allocation according to an
embodiment of the present disclosure. For the purpose of
discussion, the process 300 will be described with reference to
FIG. 1. The process 300 may involve the network device 110 and one
or more terminal devices 120 served by the network device 110.
[0045] The network device 110 determines (305) a plurality of RS
configurations based on at least one of the following: different RS
ports, or different RS sequences of a same type. As used herein, a
RS configuration is used to specify one or more aspects of
transmission of a reference signal, for example, a RS port to be
used for transmission, and/or a sequence to be generated for
transmission.
[0046] A RS port may be referred to as a specific mapping of part
or all of a RS sequence to one or more resource elements of a
resource region allocated for RS transmission in time, frequency,
and/or code domains. In some embodiments, a RS port may be defined
by a matrix representing multiple antennas multiplying by a
pre-coder matrix representing the mapping. Therefore, if one or
more certain RS ports are selected for transmission, the resource
mapping for the RS sequence can be determined. In some use cases, a
RS port may also be called as a virtual RS port or a resource
mapping between one or more antenna ports and one or more resource
elements. Generally, a plurality of different RS ports can be
specified for a certain resource region for RS transmission. These
RS ports are orthogonal to each other. Therefore, in embodiments of
the present disclosure, each of the different RS ports can be
regarded as a corresponding RS configuration.
[0047] In some embodiments, different RS sequences of a same type
can be used to define the RS configurations. For example, each of
the different RS sequences can be considered as a different RS
configuration. Generally, RS sequences of the same type may be
designed to achieve at least quasi-orthogonality. In some
embodiments, different RS sequences of the same type can be
generated based on a same generation rule. For example, different
sequences of the same type may be generated based on a same formula
with different initial value, a same formula with different root
indices, different cyclic shift values of a same root sequence,
and/or different transformations on a same sequence (for example,
frequency rotations). Various methods of sequence generations may
be utilized for generating the RS sequences based on the same root
sequence, the same initial value, the same cyclic shift, and/or the
same transformation on a sequence. In some examples, the RS
sequences may all be pseudorandom noise (PN) sequences, Zadoff-Chu
(ZC) sequences, or the like.
[0048] In some other embodiments, the RS configurations may be
defined by both RS ports and RS sequences of the same type. For
example, for two different RS configurations, the same RS port may
be assigned and then two different sequences are specified. In
other examples, for two different RS configurations, the same
sequence may be specified while different RS ports are
assigned.
[0049] The RS configurations based on the RS ports and/or RS
sequences may be preset and stored in the network device 110 for
use in some embodiments. In other embodiments, the network device
110 may determine the RS configurations dynamically (in real time)
according to a certain rule (different RS ports, or different RS
sequences, or both) when there are downlink and uplink RSs to be
transmitted.
[0050] Since the plurality of RS configurations defined by
different RS ports and/or different RS sequences of the same type
are orthogonal or at least quasi-orthogonal to each other, RS
transmissions in different links (for example, downlink and uplink)
can share these RS configurations. Specifically, the network device
110 allocates (310) at least one first RS configuration from the
plurality of RS configurations for uplink RS transmission by the
terminal device 120 and at least one second RS configuration from
the plurality of RS configurations for downlink RS transmission by
the network device 110 itself. In this sense, both downlink and
uplink RS transmissions share a common structure and can be
orthogonal or quasi-orthogonal to each other. All the first RS
configurations may be different from the second RS configurations,
or may be partially or totally overlapped with the second RS
configurations. That is, some or all of the first RS configurations
for uplink RS transmission may be the same as the second RS
configurations for downlink RS transmission.
[0051] The network device 110 may select from the plurality of RS
configurations one or more first RS configurations for uplink RS
transmission by the terminal device 120 and select one or more
second RS configurations for the downlink RS transmission by the
network device 110. In some embodiments, the network device 110 may
select different RS configurations for uplink and downlink RS
transmissions.
[0052] In some embodiments, when allocating RS configuration(s) for
the uplink RS transmission, the network device 110 may consider the
capability of the terminal device 120. The capability may be
associated with a maximum number of antenna ports or antenna
elements of the terminal device 120, and/or a maximum rank of a
channel matrix between the network device and the terminal device.
The number of the first RS configuration(s) may be less than or
equal to the maximum number of antenna ports or antenna elements or
the maximum rank of the channel matrix, in order to avoid
redundancy.
[0053] When allocating RS configuration(s) for the downlink RS
transmission, the network device 110 may also consider the
capability of a terminal device (which may be the one with uplink
RS transmission and/or another terminal device 120 served by the
network device 110). For example, the number of the second RS
configuration(s) may be less than or equal to a maximum number of
antenna ports or antenna elements of the terminal device receiving
the downlink RS, or a maximum rank of the channel matrix for the
terminal device.
[0054] In some other embodiments, in addition to sharing of the
same set of RS configurations between different links or as an
alternative, RS transmissions with different requirements (for
example, different terminal devices) can also share the determined
RS configurations. In these embodiments, the network device 110 may
allocate at least one third RS configuration from the plurality of
RS configurations for uplink RS transmission by a further terminal
device 120. For downlink RS transmissions, the network device 110
may also allocate at least one fourth RS configuration from the
plurality of RS configuration for downlink RS transmission to a
further terminal device.
[0055] To enable the terminal device 120 to transmit a RS in
uplink, the network device 110 transmits (315) to the terminal
device 120 information on the at least one first RS configuration
allocated for uplink RS transmission. The information may indicate
to the terminal device 120 one or more aspects of uplink RS
transmission as specified in the at least one first RS
configuration. For example, depending on the allocated first RS
configuration, the information may indicate to the terminal device
120 which RS port(s) and/or which RS sequence(s) are used in the
uplink RS transmission.
[0056] In some other embodiments, to reduce the overhead of
transmission of the information, the plurality of RS configurations
may have been specified or indicated to the terminal device 120 in
advance, and each of the RS configurations may be identified with
corresponding configuration parameters (for example, indexes or
identifiers). When the network device 110 determines to allocate
one or more first RS configurations for the uplink RS transmission
by the terminal device 120, the network device 110 may transmit the
corresponding configuration parameters for the allocated first RS
configurations to the terminal device 120, instead of transmitting
the detailed information on the allocated first RS
configurations.
[0057] In order to further reduce the overhead cost in indicating
the first RS configurations, the plurality of the RS configurations
may be divided into a plurality of groups with each of the groups
being identified by a corresponding group parameter (for example,
an index or identifier). For example, as shown in FIG. 4A, it is
supposed that there are totally K different RS configurations
(Config. 1 through Config. K) 410. The network device 110 may
divide these K RS configurations into L groups each including at
least one of the K RS configurations. The size of each group may be
configurable. In some embodiments, one or more of RS
configuration(s) included in one group may be the same as the RS
configurations included in another group. That is, some of the
groups may be partially overlapped with each other. In other
embodiments, some of the groups may not be overlapped.
[0058] Since a RS configuration may be dependent on RS ports or RS
sequences, FIGS. 4B and 4C also show the group division of RS ports
and RS sequences in the case of dividing the RS configuration,
where the RS ports 420 or the RS sequences 430 are divided into L
groups. In these cases, each of the groups may be identified with a
corresponding group parameter (or index, or identifier). For
example, if there are 12 RS configurations and they are divided
into 4 groups, the network device 110 may use only 2 bits to
indicate the group parameter for the allocated group to the
terminal device 120.
[0059] In the examples of FIGS. 4B and 4C, it is supposed that
there are K RS ports and RS sequences, but it will be appreciated
that the number of the RS ports and RS sequences may not be the
same. In embodiments where RS configurations are defined based on
both RS ports and RS sequences, the total number of RS
configurations may not be the same as the number of the RS ports or
RS sequences. Although the groups are shown to be divided with
consecutive RS configurations (RS ports or RS sequences), in other
examples, each of the groups may include discontinuous RS
configurations. FIG. 4D shows such an example, where each of the L
groups includes discontinuous RS ports among all the K RS ports
440.
[0060] In some embodiments, the grouping of the RS configurations
may be preset and stored in the network device 110 for use. In
other embodiments, the network device 110 may group the RS
configurations dynamically (in real time) when there are downlink
and uplink RSs to be transmitted. In these embodiments of dynamic
grouping, the network device 110 may determine each of the group
based on the sort order of the RS configurations (especially the
sort order of the RS ports). Specifically, each of the groups may
be divided with different starting indexes of the RS configurations
and/or different orders. FIGS. 4E and 4F shows examples of such
embodiments.
[0061] As shown in FIG. 4E, K RS ports 450 may be divided into L
groups. In the group division, the network device 110 may select a
starting index 451 from all the indexes of RS ports 450 for Group
1, and the order of Group 1 is as indicated by 452. Similarly, the
network device 110 may select a starting index 453 and an order 454
for Group 2, select a starting index 455 and an order 456 for Group
L-1, select a starting index 457 and an order 458 for Group L, and
the like. In some embodiments, some of the groups may be divided
according to different circular sort orders. As shown in FIG. 4F,
upon dividing the K RS ports 460, each of the L groups are divided
with different starting indexes 461, 463, 465, and the like, and
the ports included in the L groups may be selected from the K RS
ports in a clockwise circular order or an anticlockwise circular
order as indicated by 462, 464, 466, and the like. By dividing
different groups with different starting indexes and/or different
orders, in dynamical group division, the network device may be able
to obtain RS groups with less overlapped RS configurations for
uplink and downlink RS transmission for different terminal
devices.
[0062] In some further embodiments, the network device 110 may
divide all the RS configurations into two groups and allocate one
for downlink RS transmission and the other one for uplink RS
transmission. For each receiving terminal device 120 in downlink RS
transmission, the network device 110 may then be able to select one
or more of RS configurations in the group for downlink RS
transmission for the terminal device. For each transmitting
terminal device 120 in uplink RS transmission, the network device
110 may allocate one or more of RS configurations in the group for
uplink RS transmission.
[0063] Referring back to FIG. 3, upon receipt of the information on
the one or more allocated first RS configurations, the terminal
device 120 transmits (320) a first RS sequence to the network
device 110 based on the one or more allocated first RS
configurations. The terminal device 120 may determine which RS
configuration(s) will be used based on the received information and
then determine how uplink RS transmission may be performed
according to the allocated RS configuration(s). For example, if the
one or more first RS configurations indicate that the terminal
device 120 can use one or more RS ports among all the possible RS
ports, then the terminal device 120 may transmit a first RS
sequence using the corresponding RS ports. In this case, the first
RS sequence may be generated based on certain rules that are known
by both the terminal device 120 and the network device 110. As
another example, if the first RS configurations indicate that the
terminal device 120 can transmit one or more RS sequences among all
the possible RS sequences, then the terminal device 120 may
generate the corresponding RS sequence as the first RS sequences
and transmit these sequences on some or all of the possible RS
ports. In some other examples, the allocated first RS
configurations may indicate both the RS port(s) and RS sequence(s)
the terminal device 120 can used for the uplink RS
transmission.
[0064] The network device 110 may transmit (325) a second RS
sequence to the terminal device 120 based on the one or more
allocated second RS configurations. The network device 110 may
transmit the second sequence in a similar way as discussed above in
the uplink RS transmission by the terminal device 120. In some
other embodiments, the network device 120 may not transmit the
second sequence to the terminal device 120 that transmits the first
sequence in uplink, but may transmit the second sequence to a
further terminal device served by the network device 110.
[0065] In some embodiments, as a receiving side in the downlink RS
transmission, a terminal device 120 may be interfered by uplink RS
transmission by other terminal devices 120 and/or downlink RS
transmission intended for other terminal devices 120. In these
cases, the network device 110 may transmit to a terminal device 120
information on RS configurations allocated for uplink RS
transmission by other terminal devices 120 and/or for downlink RS
transmission to be performed by the network device 120. Such
information may be transmitted in a similar way as discussed at 315
with reference to FIG. 2. With the received information, the
terminal device 120 may perform interference cancellation and other
operations to further improve the quality of the received downlink
RS. Various technologies that are currently used and to be
developed in the future may be utilized for the interference
cancellation based on the received information.
[0066] As a receiving side in the uplink RS transmission, the
network device 110 may interfere in uplink RS transmission and
downlink RS transmission of a neighboring network device in a
neighboring cell. In this case, the network device 110 may transmit
information on RS configurations allocated for current downlink and
uplink RS transmissions in its serving cell to the network device
located in the neighboring cell. The network device 110 may also
receive similar information provided by the neighboring network
device and utilize the information for interference
cancellation.
[0067] In transmission of uplink and downlink reference signals by
the network device 110 and the terminal device 120, the reference
signals may be multiplexed in the resource region according to the
communication techniques to be employed and the RS configurations
that are allocated. FIG. 5A to 5D shows illustrative diagram of
multiplexing of two different reference signals on a resource
region (time and frequency). These two different reference signals
may be transmitted in an uplink and a downlink, or transmitted by
different terminal device in uplinks.
[0068] In FIG. 5A, a Frequency Division Multiple (FDM) technique is
applied and thus two reference signals 510 and 520 are multiplexed
in a physical resource block using different frequency resources.
In FIG. 5B, an Interleaved Frequency Division Multiple Access
(IFDMA) technique is applied and two reference signals 512 and 522
are interleaved in frequency domain. As shown in FIG. 5C, a Time
Division Multiple (TDM) technique is applied and two reference
signals 514 and 524 are multiplexed in time domain. In another
example of FIG. 5D, two different signals 516 and 526 are divided
in two PRBs according to the FDM techniques.
[0069] In some embodiments, the network device 110 may allocate the
RS configurations periodically or upon request. In some
embodiments, after the RS configurations are allocated for the
uplink and downlink transmission, the network device 110 and/or the
terminal device 120 may keep using the allocated RS configurations
to transmit downlink and uplink RS sequences for a period of time.
During this period of time, if the uplink or downlink transmission
need more resources to be transmitted and additional RS
configurations are not allocated, the network device 110 may employ
other manners to support the uplink or downlink RS
transmission.
[0070] In one embodiment, more RS ports allocated for other RS
transmission may be configured and applied. As shown in FIG. 6A, if
two reference signals 510 and 520 are previously mapped in a
resource region as shown in FIG. 5A and the reference signal 510
needs more resource to be transmitted, then the reference signal
510 may be allowed to be transmitted in frequency allocated for the
reference signal 520.
[0071] In another embodiment, as shown in FIG. 6B, different RS
sequences 602 and 604 may be allocated for this reference signal
510 for transmission in the same frequency region. In yet another
embodiment, the more orthogonal cover codes (in time or frequency
domain) may be used with more resources (more RS ports), as shown
in FIG. 6C.
[0072] In further embodiments, the resource mapping for the
reference signals may be less density in time, frequency, or code
domain and more RS ports can be used so as to meet the requirement
for the transmission of the reference signals. For example, as
shown in FIG. 6D, the reference signals 510 and 520 occupy more
frequency resources (it would be appreciated that the reference
signal 520 may not necessarily be allocated with more resources if
the previously allocated resources are enough for its
transmission).
[0073] The RS configuration allocation has been discussed above.
According to various embodiments of the present disclosure, RS
configurations are defined/specified based on RS ports and/or RS
sequences and can be shared by downlink and uplink RS transmissions
of the network device and different terminal devices, which support
flexible and dynamic RS configuration allocation for both downlink
and uplink RS transmissions. The RS configuration allocation can
satisfies some new requirements on the downlink and uplink RS
transmissions, achieving a common structure and orthogonality for
both downlink and uplink RS transmissions.
[0074] FIG. 7 shows a flowchart of an example method 700 in
accordance with some embodiments of the present disclosure. The
method 700 can be implemented at a network device 110 as shown in
FIG. 1. For the purpose of discussion, the method 700 will be
described from the perspective of the network device 110 with
reference to FIG. 1.
[0075] At block 710, the network device 110 determines a plurality
of reference signal (RS) configurations based on at least one of
the following: different RS ports, or different RS sequences of a
same type. At block 720, the network device 110 allocates at least
one first RS configuration from the plurality of RS configurations
for uplink RS transmission by a terminal device served by the
network device, and at block 730, the network device 110 allocates
at least one second RS configuration from the plurality of RS
configurations for downlink RS transmission by the network
device.
[0076] In some embodiments, the method 700 may further include
transmitting to the terminal device information on the at least one
first RS configuration, and receiving a first RS sequence from the
terminal device based on the at least one first RS
configuration.
[0077] In some embodiments, allocating the at least one first RS
configuration may include dividing the plurality of RS
configurations into a plurality of groups, each of the plurality of
groups being identified by a group parameter, and selecting a first
group from the plurality of groups for the uplink RS transmission,
the first group including the at least one first RS configuration.
Transmitting the information may include transmitting the group
parameter for the first group to the terminal device.
[0078] In some embodiments, the first RS sequence may include at
least one of a demodulation reference signal (DMRS) sequence, a
channel state information-reference signal (CSI-RS) sequence, or a
sounding reference signal (SRS) sequence.
[0079] In some embodiments, the method 700 may further include
transmitting a second RS sequence to a further terminal device
served by the network device based on the at least one second RS
configuration, and transmitting to the further terminal device
information on the at least one first RS configuration.
[0080] In some embodiments, allocating the at least one first RS
configuration to the terminal device may include allocating the at
least one first RS configuration to the terminal device based on
capability of the terminal device, the capability being associated
with at least one of a maximum number of antenna ports or antenna
elements of the terminal device, or a maximum rank of a channel
matrix between the network device and the terminal device.
[0081] In some embodiments, the different RS sequences are to be
generated based on different root sequences, different initial
values, different cyclic shifts, or different transformations on a
sequence.
[0082] In some embodiments, the method 700 may further include
allocating at least one third RS configuration from the plurality
of RS configurations for uplink RS transmission by a further
terminal device served by the network device.
[0083] FIG. 8 shows a flowchart of an example method 800 in
accordance with some embodiments of the present disclosure. The
method 800 can be implemented at a terminal device 120 as shown in
FIG. 1. For the purpose of discussion, the method 800 will be
described from the perspective of the terminal device 120 with
reference to FIG. 1.
[0084] At block 810, the terminal device 120 receives from a
network device information on at least one first RS configuration
among a plurality of reference signal (RS) configurations. The
plurality of RS configurations are determined based on at least one
of the following: different RS ports, or different RS sequences of
a same type, and at least one second RS configuration among the
plurality of RS configurations being allocated for downlink RS
transmission by the network device. At block 820, the terminal
device 120 transmits a RS sequence to the network device based on
the at least one first RS configuration.
[0085] In some embodiments, the plurality of RS configurations may
be divided into a plurality of groups, each of the plurality of
groups being identified by a group parameter. Receiving the
information may include receiving from the network device the group
parameter for a first group of the plurality of groups, the first
group including the at least one first RS configuration.
[0086] In some embodiments, the RS sequence may include at least
one of a demodulation reference signal (DMRS) sequence, a channel
state information-reference signal (CSI-RS) sequence, or a sounding
reference signal (SRS) sequence.
[0087] In some embodiments, the method 800 may further include
receiving from the network device information on at least one third
RS configuration, the at least one third RS configuration being
allocated by the network device to a further terminal device for
uplink RS transmission; receiving a further RS sequence transmitted
by the network device based on the at least one second RS
configuration; and applying interference cancellation for the
further RS sequence based on the information on the at least one
third RS configuration.
[0088] In some embodiments, the different RS sequences may be to be
generated based on different root sequences, different initial
values, different cyclic shifts, or different transformations on a
sequence.
[0089] It is to be understood that all operations and features
related to the network device 110 and terminal device 120 described
above with reference to FIGS. 3-6D are likewise applicable to the
methods 700 and 800 and have similar effects. For the purpose of
simplification, the details will be omitted.
[0090] FIG. 9 shows a block diagram of an apparatus 900 in
accordance with some embodiments of the present disclosure. The
apparatus 900 can be considered as an example implementation of the
network device 110 as shown in FIG. 1. As shown, the apparatus 900
includes a determining unit 910 configured to determine a plurality
of reference signal (RS) configurations based on at least one of
the following: different RS ports, or different RS sequences of a
same type. The apparatus 900 also includes a first allocating unit
920 configured to allocate at least one first RS configuration from
the plurality of RS configurations for uplink RS transmission by a
terminal device served by the network device, and a second
allocating unit 930 configured to allocate at least one second RS
configuration from the plurality of RS configurations for downlink
RS transmission by the network device.
[0091] In some embodiments, the apparatus 900 may further a
transmitting unit configured to transmit to the terminal device
information on the at least one first RS configuration, and a
receiving unit configured to receive a first RS sequence from the
terminal device based on the at least one first RS
configuration.
[0092] In some embodiments, the first allocating unit 920 may be
configured to divide the plurality of RS configurations into a
plurality of groups, each of the plurality of groups being
identified by a group parameter, and select a first group from the
plurality of groups for the uplink RS transmission, the first group
including the at least one first RS configuration. The transmitting
unit may be configured to transmit the information comprises
transmitting the group parameter for the first group to the
terminal device.
[0093] In some embodiments, the first RS sequence may include at
least one of a demodulation reference signal (DMRS) sequence, a
channel state information-reference signal (CSI-RS) sequence, or a
sounding reference signal (SRS) sequence.
[0094] In some embodiments, the apparatus 900 may include a further
transmitting unit configured to transmit a second RS sequence to a
further terminal device served by the network device based on the
at least one second RS configuration, and to transmit to the
further terminal device information on the at least one first RS
configuration.
[0095] In some embodiments, the first allocating unit 920 may be
configured to allocate the at least one first RS configuration to
the terminal device based on capability of the terminal device, the
capability being associated with at least one of a maximum number
of antenna ports or antenna elements of the terminal device, or a
maximum rank of a channel matrix between the network device and the
terminal device.
[0096] In some embodiments, the different RS sequences may be to be
generated based on different root sequences, different initial
values, different cyclic shifts, or different transformations on a
sequence.
[0097] In some embodiments, the apparatus 900 may a third
allocating unit configured to allocate at least one third RS
configuration from the plurality of RS configurations for uplink RS
transmission by a further terminal device served by the network
device.
[0098] FIG. 10 shows a block diagram of an apparatus 1000 in
accordance with some embodiments of the present disclosure. The
apparatus 1000 can be considered as an example implementation of
the terminal device 120 as shown in FIG. 1. As shown, the apparatus
1000 includes a receiving unit 1010 configured to receive from a
network device information on at least one first RS configuration
among a plurality of reference signal (RS) configurations, the
plurality of RS configurations being determined based on at least
one of the following:
[0099] different RS ports, or different RS sequences of a same
type, and at least one second RS configuration among the plurality
of RS configurations being allocated for downlink RS transmission
by the network device. The apparatus 1000 also includes a
transmitting unit 1020 configured to transmit a RS sequence to the
network device based on the at least one first RS
configuration.
[0100] In some embodiments, the plurality of RS configurations may
be divided into a plurality of groups, each of the plurality of
groups being identified by a group parameter. Receiving the
information may include receiving from the network device the group
parameter for a first group of the plurality of groups, the first
group including the at least one first RS configuration.
[0101] In some embodiments, the RS sequence may include at least
one of a demodulation reference signal (DMRS) sequence, a channel
state information-reference signal (CSI-RS) sequence, or a sounding
reference signal (SRS) sequence.
[0102] In some embodiments, the receiving unit 1010 may be
configured to receive from the network device information on at
least one third RS configuration, the at least one third RS
configuration being allocated by the network device to a further
terminal device for uplink RS transmission, and receive a further
RS sequence transmitted by the network device based on the at least
one second RS configuration. The apparatus 1000 further includes an
interference cancelling unit configured to apply interference
cancellation for the further RS sequence based on the information
on the at least one third RS configuration.
[0103] In some embodiments, the different RS sequences may be to be
generated based on different root sequences, different initial
values, different cyclic shifts, or different transformations on a
sequence.
[0104] It should be appreciated that units included in the
apparatuses 900 and 1000 corresponds to the blocks of the method
700 as well as the method 800. Therefore, all operations and
features described above with reference to FIGS. 3-6D are likewise
applicable to the units included in the apparatuses 900 and 1000
and have similar effects. For the purpose of simplification, the
details will be omitted.
[0105] The units included in the apparatuses 900 and 1000 may be
implemented in various manners, including software, hardware,
firmware, or any combination thereof. In one embodiment, one or
more units may be implemented using software and/or firmware, for
example, machine-executable instructions stored on the storage
medium. In addition to or instead of machine-executable
instructions, parts or all of the units in the apparatuses 900 and
1000 may be implemented, at least in part, by one or more hardware
logic components. For example, and without limitation, illustrative
types of hardware logic components that can be used include
Field-programmable Gate Arrays (FPGAs), Application-specific
Integrated Circuits (ASICs), Application-specific Standard Products
(ASSPs), System-on-a-chip systems (SOCs), Complex Programmable
Logic Devices (CPLDs), and the like.
[0106] FIG. 11 is a simplified block diagram of a device 1100 that
is suitable for implementing embodiments of the present disclosure.
The device 1100 can be considered as a further example
implementation of a network device 110 or a terminal device 120 as
shown in FIG. 1. Accordingly, the device 1100 can be implemented at
or as at least a part of the network device 110 or the terminal
device 120.
[0107] As shown, the device 1100 includes a processor 1110, a
memory 1120 coupled to the processor 1110, a suitable transmitter
(TX) and receiver (RX) 1140 coupled to the processor 1110, and a
communication interface coupled to the TX/RX 1140. The memory 1110
stores at least a part of a program 1130. The TX/RX 1140 is for
bidirectional communications. The TX/RX 1140 has at least one
antenna to facilitate communication, though in practice an Access
Node mentioned in this application may have several ones. The
communication interface may represent any interface that is
necessary for communication with other network elements, such as X2
interface for bidirectional communications between eNBs, S1
interface for communication between a Mobility Management Entity
(MME)/Serving Gateway (S-GW) and the eNB, Un interface for
communication between the eNB and a relay node (RN), or Uu
interface for communication between the eNB and a terminal
device.
[0108] The program 1130 is assumed to include program instructions
that, when executed by the associated processor 1110, enable the
device 1100 to operate in accordance with the embodiments of the
present disclosure, as discussed herein with reference to FIGS. 3
to 6D. The embodiments herein may be implemented by computer
software executable by the processor 1110 of the device 1100, or by
hardware, or by a combination of software and hardware. The
processor 1110 may be configured to implement various embodiments
of the present disclosure. Furthermore, a combination of the
processor 1110 and memory 1110 may form processing means 1150
adapted to implement various embodiments of the present
disclosure.
[0109] The memory 1110 may be of any type suitable to the local
technical network and may be implemented using any suitable data
storage technology, such as a non-transitory computer readable
storage medium, semiconductor based memory devices, magnetic memory
devices and systems, optical memory devices and systems, fixed
memory and removable memory, as non-limiting examples. While only
one memory 1110 is shown in the device 1100, there may be several
physically distinct memory modules in the device 1100. The
processor 1110 may be of any type suitable to the local technical
network, and may include one or more of general purpose computers,
special purpose computers, microprocessors, digital signal
processors (DSPs) and processors based on multicore processor
architecture, as non-limiting examples. The device 1100 may have
multiple processors, such as an application specific integrated
circuit chip that is slaved in time to a clock which synchronizes
the main processor.
[0110] Generally, various embodiments of the present disclosure may
be implemented in hardware or special purpose circuits, software,
logic or any combination thereof. Some aspects may be implemented
in hardware, while other aspects may be implemented in firmware or
software which may be executed by a controller, microprocessor or
other computing device. While various aspects of embodiments of the
present disclosure are illustrated and described as block diagrams,
flowcharts, or using some other pictorial representation, it will
be appreciated that the blocks, apparatus, systems, techniques or
methods described herein may be implemented in, as non-limiting
examples, hardware, software, firmware, special purpose circuits or
logic, general purpose hardware or controller or other computing
devices, or some combination thereof.
[0111] The present disclosure also provides at least one computer
program product tangibly stored on a non-transitory computer
readable storage medium. The computer program product includes
computer-executable instructions, such as those included in program
modules, being executed in a device on a target real or virtual
processor, to carry out the process or method as described above
with reference to any of FIGS. 3 to 6D. Generally, program modules
include routines, programs, libraries, objects, classes,
components, data structures, or the like that perform particular
tasks or implement particular abstract data types. The
functionality of the program modules may be combined or split
between program modules as desired in various embodiments.
Machine-executable instructions for program modules may be executed
within a local or distributed device. In a distributed device,
program modules may be located in both local and remote storage
media.
[0112] Program code for carrying out methods of the present
disclosure may be written in any combination of one or more
programming languages. These program codes may be provided to a
processor or controller of a general purpose computer, special
purpose computer, or other programmable data processing apparatus,
such that the program codes, when executed by the processor or
controller, cause the functions/operations specified in the
flowcharts and/or block diagrams to be implemented. The program
code may execute entirely on a machine, partly on the machine, as a
stand-alone software package, partly on the machine and partly on a
remote machine or entirely on the remote machine or server.
[0113] The above program code may be embodied on a machine readable
medium, which may be any tangible medium that may contain, or store
a program for use by or in connection with an instruction execution
system, apparatus, or device. The machine readable medium may be a
machine readable signal medium or a machine readable storage
medium. A machine readable medium may include but not limited to an
electronic, magnetic, optical, electromagnetic, infrared, or
semiconductor system, apparatus, or device, or any suitable
combination of the foregoing. More specific examples of the machine
readable storage medium would include an electrical connection
having one or more wires, a portable computer diskette, a hard
disk, a random access memory (RAM), a read-only memory (ROM), an
erasable programmable read-only memory (EPROM or Flash memory), an
optical fiber, a portable compact disc read-only memory (CD-ROM),
an optical storage device, a magnetic storage device, or any
suitable combination of the foregoing.
[0114] Further, while operations are depicted in a particular
order, this should not be understood as requiring that such
operations be performed in the particular order shown or in
sequential order, or that all illustrated operations be performed,
to achieve desirable results. In certain circumstances,
multitasking and parallel processing may be advantageous. Likewise,
while several specific implementation details are contained in the
above discussions, these should not be construed as limitations on
the scope of the present disclosure, but rather as descriptions of
features that may be specific to particular embodiments. Certain
features that are described in the context of separate embodiments
may also be implemented in combination in a single embodiment.
Conversely, various features that are described in the context of a
single embodiment may also be implemented in multiple embodiments
separately or in any suitable sub-combination.
[0115] Although the present disclosure has been described in
language specific to structural features and/or methodological
acts, it is to be understood that the present disclosure defined in
the appended claims is not necessarily limited to the specific
features or acts described above. Rather, the specific features and
acts described above are disclosed as example forms of implementing
the claims.
* * * * *