U.S. patent number 9,271,266 [Application Number 12/451,350] was granted by the patent office on 2016-02-23 for searching for control channels in a wireless network.
This patent grant is currently assigned to WIRELESS FUTURE TECHNOLOGIES INC.. The grantee listed for this patent is Frank Frederiksen, Troels Emil Kolding. Invention is credited to Frank Frederiksen, Troels Emil Kolding.
United States Patent |
9,271,266 |
Frederiksen , et
al. |
February 23, 2016 |
Searching for control channels in a wireless network
Abstract
A user equipment (UE) may receive an OFDM signal having control
channel elements (CCEs). The CCEs may be arranged in levels where a
first level aggregates less CCEs than a second level. A processor
may search for a control channel from control channel candidates
that is comprised of the CCEs. A limited number of CCEs may be
searched on the first level.
Inventors: |
Frederiksen; Frank (Klarup,
DK), Kolding; Troels Emil (Klarup, DK) |
Applicant: |
Name |
City |
State |
Country |
Type |
Frederiksen; Frank
Kolding; Troels Emil |
Klarup
Klarup |
N/A
N/A |
DK
DK |
|
|
Assignee: |
WIRELESS FUTURE TECHNOLOGIES
INC. (Ottawa, Ontario, CA)
|
Family
ID: |
38626484 |
Appl.
No.: |
12/451,350 |
Filed: |
May 6, 2008 |
PCT
Filed: |
May 06, 2008 |
PCT No.: |
PCT/EP2008/055557 |
371(c)(1),(2),(4) Date: |
March 02, 2010 |
PCT
Pub. No.: |
WO2008/135575 |
PCT
Pub. Date: |
November 13, 2008 |
Prior Publication Data
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|
|
Document
Identifier |
Publication Date |
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US 20100208666 A1 |
Aug 19, 2010 |
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Foreign Application Priority Data
|
|
|
|
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May 7, 2007 [EP] |
|
|
07107652 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04W
72/0406 (20130101); H04B 7/2637 (20130101); H04W
72/042 (20130101); H04L 5/0051 (20130101); H04W
52/0209 (20130101); H04J 11/00 (20130101); H04W
88/02 (20130101); Y02D 30/70 (20200801); Y02B
70/30 (20130101) |
Current International
Class: |
H04W
4/00 (20090101); H04W 72/04 (20090101); H04B
7/216 (20060101); H04B 7/26 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0575281 |
|
Nov 1999 |
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EP |
|
1313228 |
|
May 2003 |
|
EP |
|
2003-0041468 |
|
May 2003 |
|
KR |
|
2006-0039865 |
|
May 2006 |
|
KR |
|
2216107 |
|
Nov 2003 |
|
RU |
|
2280951 |
|
Jul 2006 |
|
RU |
|
2007/051186 |
|
May 2007 |
|
WO |
|
Other References
J Zyren; "Overview of the 3GPP Long Term Evolution Physical Layer";
White Paper from freescale semiconductor, Jul. 2007; pp. 1-25.
cited by applicant .
Physical Channel Structure and Procedure for EUTRA Downlink; 3GPP
TSG-RAN WG1 Meeting #42, Tdoc R1-050884; Sep. 2005; pp. 1-18. cited
by applicant .
"E-UTRA Downlink Control Channel Structure and TP"; 3GPP TSG
RAN1#44 R1-06378; Feb. 2006; 7 pp. cited by applicant .
"EUTRA SC-FDMA Uplink Resource Block, Resource Allocation and
Pilot/Reference Signal Design & TP"; 3GPP TSG RANI LTE Ad Hoc;
R1-060246; Jan. 2006; pp. 1-18. cited by applicant .
Universal Mobile Telecommunications System (UMTS): Evolved
Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal
Terrestrial Radio Access Network (E-UTRAN); Overall description;
Stage 2 (3GPP TS 36.300 V 8.0.0 Release 8) 3rd Generation
Partnership Project; Technical Spec Group Radio Access Network,
Mar. 2007; pp. 1-83. cited by applicant .
International Search Report for Application No. PCT/EP2008/05557;
mailed Sep. 15, 2008. cited by applicant .
European Search Report for Application No. EP07107652.5-1249; dated
Nov. 27, 2007. cited by applicant .
"3rd Generation Partnership Project; Technical Specification Group
Radio Access Network; Physical Layer Procedures", Release 8, 3GPP
TS 36.213, V1.0.0, Mar. 2007, pp. 1-11. cited by applicant .
Notice of Allowance issued Dec. 19, 2011 in corresponding Korean
Application No. 10-2009-7025561. cited by applicant .
Office Action issued Mar. 26, 2013 in corresponding Russian
Application No. 2009145117/07. cited by applicant .
English Abstract of Korean Patent Application No. 2006-0039865
dated May 9, 2006. cited by applicant .
Third Generation Partnership Project, "Technical Specification
Group Radio Access Network; Multiplexing and channel coding
(Release 8)," 3GPP TS 36.212 V1.0.0 (Mar. 2007). cited by applicant
.
Third Generation Partnership Project, "Technical Specification
Group Radio Access Network; Physical Channels and Modulation
(Release 8)," 3GPP TS 36.211 V1.0.0 (Mar. 2007). cited by
applicant.
|
Primary Examiner: Nguyen; Steven H
Attorney, Agent or Firm: Volpe and Koenig, P.C.
Claims
The invention claimed is:
1. A method of operating a user equipment, the method comprising:
receiving a wireless signal at the user equipment, the wireless
signal comprising a control channel for the user equipment, the
control channel being in at least one control channel element
(CCE), the control channel comprising an indication of an uplink
communication resource useable by the user equipment for uplink
communication; searching for the control channel in the at least
one CCE from a plurality of candidate CCEs, the plurality of
candidate CCEs being in a plurality of aggregation levels, each of
the plurality of aggregation levels comprising a respective limited
number of candidate control channels, and the searching includes
searching at least one of the respective limited number of
candidate control channels in at least one of the plurality of
aggregation levels; and transmitting an uplink data signal
according to the uplink communication resource, the indication of
the uplink communication resource decoded from the control channel
of the wireless signal according to the plurality of candidate CCEs
using an identifier associated with the user equipment.
2. The method of claim 1, wherein at a first aggregation level the
control channel is in one CCE and wherein at a second aggregation
level the control channel is in two consecutive CCEs.
3. The method of claim 2, wherein at a third aggregation level the
control channel is in four consecutive CCEs and wherein at a fourth
aggregation level the control channel is in eight consecutive
CCEs.
4. The method of claim 1, wherein the searching further comprises:
decoding the plurality of candidate CCEs using the identifier
associated with the user equipment to determine the uplink
communication resource.
5. A user equipment comprising: a receiver operable to receive a
wireless signal at the user equipment, the wireless signal
comprising a control channel for the user equipment, the control
channel being in at least one control channel element (CCE),
wherein the control channel comprises an indication of an uplink
communication resource useable by the user equipment for uplink
communication; a processor operable to search for the control
channel in the at least one CCE from a plurality of candidate CCEs,
the plurality of candidate CCEs being in a plurality of aggregation
levels, each of the plurality of aggregation levels comprising a
respective limited number of candidate control channels, and the
searching includes searching at least one of the respective limited
number of candidate control channels in at least one of the
plurality of aggregation levels; and a transmitter operable to
transmit an uplink data signal according to the uplink
communication resource, the indication of the uplink communication
resource decoded from the control channel of the wireless signal
according to the plurality of candidate CCEs using an identifier
associated with the user equipment.
6. The user equipment of claim 5, wherein at a first aggregation
level the control channel is in one CCE and wherein at a second
aggregation level the control channel is in two consecutive
CCEs.
7. The user equipment of claim 6, wherein at a third aggregation
level the control channel is in four consecutive CCEs and wherein
at a fourth aggregation level the control channel is in eight
consecutive CCEs.
8. The user equipment of claim 5, wherein the processor is further
operable to decode the plurality of candidate CCEs using the
identifier associated with the user equipment to determine the
uplink communication resource.
9. A non-transitory computer readable storage medium storing a set
of instructions for execution by a user equipment, the set of
instructions comprising: a receiving code segment for receiving a
wireless signal at the user equipment, the wireless signal
comprising a control channel for the user equipment, the control
channel being in at least one control channel element (CCE), the
control channel comprising an indication of an uplink communication
resource useable by the user equipment for uplink communication; a
searching code segment for searching for the control channel in the
at least one CCE from a plurality of candidate CCEs, the plurality
of candidate CCEs being in a plurality of aggregation levels, each
of the plurality of aggregation levels comprising a respective
limited number of candidate control channels, and the searching
includes searching at least one of the respective limited number of
candidate control channels in at least one of the plurality of
aggregation levels; and a transmitting code segment for
transmitting an uplink data signal according to the uplink
communication resource, the indication of the uplink communication
resource decoded from the control channel of the wireless signal
according to the plurality of candidate CCEs using an identifier
associated with the user equipment.
10. The non-transitory computer readable medium of claim 9, wherein
at a first aggregation level the control channel is in one CCE and
wherein at a second aggregation level the control channel is in two
consecutive CCEs.
11. The non-transitory computer readable medium of claim 10,
wherein at a third aggregation level the control channel is in four
consecutive CCEs and wherein at a fourth aggregation level the
control channel is in eight consecutive CCEs.
12. The non-transitory computer readable medium of claim 9, wherein
the searching code segment includes instructions for decoding the
plurality of candidate CCEs using the identifier associated with
the user equipment to determine the uplink communication resource.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
This application is the U.S. national stage of International
Application No. PCT/EP2008/055557, filed May 6, 2008 and claims the
benefit thereof. The International Application claims the benefits
of European Application No. 07107652 filed on May 7, 2007, both
applications are incorporated by reference herein in their
entirety.
BACKGROUND
The method described below relates to control channels in
communication network systems, and in particular to control channel
allocation and decoding e.g. in 3GPP (3.sup.rd Generation
Partnership Project) LTE (Long Term Evolution) network systems.
LTE technology, for example, defines a packet radio system, where
all channel allocations are expected to happen in short periods of
sub-frames. This is contrary to the older 3G systems, where
dedicated signalling channels are necessary to be set up even for
packet traffic. It is also different from WLAN (Wireless Local Area
Network) type of allocations, where each IP (Internet Protocol)
packet transmission contains a transport header.
According to LTE technology, all allocations are signalled in
Shared Control Channels, which are present in first multi-carrier
symbols of a sub-frame preceding multi-carrier symbols of data
channels. The control channels are separately coded. That is, a
downlink (or uplink) channel is divided into two separate parts,
one for control and one for data. The data part (PDSCH) carries
downlink (or uplink) data for simultaneously scheduled users, while
the control part (PDCCH) carries (among others) allocation
information for the scheduled users.
SUMMARY
The methods and devices described below are for reducing control
channel decoding complexity. The method may be implemented as a
computer program product.
Accordingly, a tree search for aggregated control channels is
reduced in a systematic way, which will obtain a significant
reduction of the number of decoding attempts at a UE (User
Equipment) side, while still maintaining most of the scheduling
flexibility in an eNB (evolved Node B), i.e. system spectral
efficiency versus UE complexity trade-off is obtained.
Accordingly it is assumed that there will not be a large amount of
users having the same propagation conditions being scheduled at the
same time. The tree reduction is obtained by putting some
limitations on the tree structure through specifications.
The UE utilizes the tree structure to reduce the decoding
complexity in order to save power. According to an embodiment,
power consumption in the decoding/detection of an L1/L2 control
channel can be reduced.
For the purpose of the methods and devices described herein below,
it should be noted that a user equipment may for example be any
device by which a user may access a communication network; this
implies mobile as well as non-mobile devices and networks,
independent of the technology platform on which they are based; a
user equipment can act as a client entity or as a server entity, or
may even have both functionalities integrated therein; methods
likely to be implemented as software code portions and being run
using a processor at one of the server/client entities are software
code independent and can be specified using any known or future
developed programming language; methods and/or devices likely to be
implemented as hardware components at one of the server/client
entities are hardware independent and can be implemented using any
known or future developed hardware technology or any hybrids of
these, such as MOS, CMOS, BiCMOS, ECL, TTL, etc, using for example
ASIC components or DSP components, as an example; generally, any
method is suitable to be implemented as software or by hardware
without changing the idea of the present invention; devices can be
implemented as individual devices, but this does not exclude that
they are implemented in a distributed fashion throughout the
system, as long as the functionality of the device is
preserved.
The method is not limited to LTE network systems, but can be
applied to any other communication systems requiring dynamic and
fast channel allocation, including systems where there will be
multiple code rates for the control channel.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other aspects and advantages will become more apparent
and more readily appreciated from the following description of the
exemplary embodiments, taken in conjunction with the accompanying
drawings of which:
FIG. 1 is an example of a tree structure with three allocated nodes
in different levels of the tree.
FIG. 2 is a data structure diagram of the three allocated nodes of
FIG. 1 mapped to sub-carrier resources in a distributed manner.
FIG. 3 is a matrix diagram illustrating a combination of control
channel elements to create aggregated control channel
candidates.
FIG. 4 is a data structure diagram of an example illustrating
reduction of possible aggregation options for control channel
candidates according to an embodiment.
FIG. 5 is a schematic block diagram illustrating functions of a
user equipment and a network device according to an embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Reference will now be made in detail to the preferred embodiments,
examples of which are illustrated in the accompanying drawings,
wherein like reference numerals refer to like elements
throughout.
A Physical Downlink Shared Control Channel (PDSCCH) which carries
(among others) allocation information for simultaneously scheduled
users of a communication network system is arranged to a tree
structure having of multiple control channel elements as shown in
FIG. 1. During decoding, a UE (User Equipment) will combine or
aggregate the control channel elements to create different code
blocks or control channel candidates. Each code block is called a
control channel candidate as it potentially carries information for
one MAC (Medium Access Control) ID. The MAC ID is used by the UE or
by a group of UEs to detect the channel. At each level of the tree,
each node represents a single control channel of a code block. The
number of the control channels at the lowest level of the tree is
determined by the system bandwidth and number of OFDM symbols n
available for the largest code blocks, as well as the size of the
control channel elements. In the example shown in FIG. 1, n=3. Any
node of the tree, which is not occupied by a control channel in
this level, is available for the next level of the tree as two
control channels, each of which are half of the size of the control
channel at the parent node.
The system bandwidth of a given number of sub-carrier resources may
be divided to an integer multiple of the largest control channels.
A given node of the tree, i.e., a set of sub-carriers, can be one
control channel of the largest code block, of up to two control
channels of the second largest code blocks or up to four control
channels of the smallest code blocks.
Each control channel extends entirely over the first n OFDM
symbols, which are available for the control channels. The control
channels may be distributed to the sub-carriers over the system
bandwidth to maximize the frequency diversity. For example, there
are 4 distributed sets of sub-carrier resources allocated per each
code-block. This is illustrated in FIG. 2.
In FIG. 1, three allocated nodes CB1, CB2, CB3 in different levels
of the tree structure are shown. FIG. 2 shows the three allocated
nodes CB1, CB2, CB3 mapped to the sub-carrier resources in a
distributed manner. It should be noted that these mappings are only
examples, and that the mapping in general should provide frequency
diversity by scattering over the system bandwidth.
As each control channel has to be uniquely identified by a MAC ID,
it can be combined to CRC (Cyclic Redundancy Code) by partly
masking CRC bits with the MAC-ID. As the MAC ID is used for
addressing both UE specific control channels and common control
channels, it is reasonable to define the MAC ID in a compatible
way. Thus, reception of any control channel is possible by
filtering control channels with the respective MAC ID. Error
detection is available from the MAC ID masked CRC. The length of
the MAC ID is matched to the C-RNTI (Cell Radio Network Temporary
Identifier) length.
A receiver, e.g. the UE, receives symbols of the Downlink Shared
Control Channel part of the sub-frame prior to reception and
processing of the symbols in the downlink and uplink Shared Data
Channels. The receiver demodulates and decodes the sub-carriers of
the OFDM symbols in which the receiver may search for a set of
largest code blocks, e.g. CB1 of FIG. 1. As the Code Block is of
known size and the system bandwidth is known, the receiver knows an
integer multiple of sub-carrier positions to search for a CB1. The
reception, whether correctly detected or not, may be recognized by
Cyclic Redundancy Check detector filtered by a receiver specific
c-RNTI identity. For every match of CRC, to which the c-RNTI of the
UE does not match, the receiver knows that the next higher level of
tree is masked and not available. For every non-matched CRC check,
the UE will continue decoding code blocks (CB2) in the next higher
level of the tree searching for a match in two child nodes of the
parent node. Further on, for every non-matched CRC check, the UE
will continue decoding code blocks (CB3) in the next higher level
of the tree searching for a match in two child nodes of the parent
node. The search continues until the UE has detected and correctly
decoded all control channels, intended for its reception.
In addition to search signalling entries with its own receiver
specific c-RNTI, the UE may have to search for common signalling
entries by common identifiers.
The search in the tree may happen in any other order than from the
lowest level node towards the higher level nodes. Depending on the
applied coding scheme, the receiver may process the nodes from the
highest level of nodes to the lower level of nodes. Further on, the
receiver may process the nodes in other arbitrary (or systematic)
order based on some measures e.g. SINR (Signal Interference and
Noise Ratio) quality of the candidate code block(s).
In the following it is assumed that only a single size of a node
(i.e. control channel) at the highest level of the tree structure
(level 3 in FIG. 1) is defined for a given bandwidth in a cell. The
highest level node is referred to as "control channel element".
Aggregation of multiple control channel elements can be used to get
larger payloads and/or lower coding rate.
However, the aggregation of the control channel elements may
require a large number of decoding attempts from all the UEs that
are listening for a possible allocation. An example of a control
channel aggregation is shown in FIG. 3.
From FIG. 3 it can be seen that an aggregation of even a relative
low number of control channel elements will result in a rather high
number of decoding attempts for the UEs listening for resource
allocations, and each UE will listen for downlink allocations as
well as uplink allocations. In the example in FIG. 3, there are 6
control channel elements, while the aggregation using a tree
structure as shown in FIG. 1 results in 10 potential control
channel candidates. This is suboptimal regarding UE complexity, as
a UE will have to decode the full amount of control channel
candidates even if some of them are not scheduled.
In the following an embodiment will described in greater
detail.
FIG. 4 shows a kind of flat tree structure arising from FIG. 3.
FIG. 4 illustrates potential control channel candidates for
different aggregation possibilities (both the white and grey
areas). As can be seen from FIG. 4, there is a total of 24 control
channel elements (CCEs), which by default triggers 45 decoding
attempts per link direction (i.e. downlink/uplink) allocation. In
other words, in aggregation level 1 the 24 control channel elements
each may form a control channel. In aggregation level 2, two
control channel elements may be aggregated to form a control
channel, in aggregation level 4, four control channel elements may
be aggregated to form a control channel, and in aggregation level
8, eight control channel elements may be aggregated to form a
control channel.
According to an embodiment, the control channel structure shown by
the white and grey areas in FIG. 4 is put under limitations, such
that only the white aggregated control channel candidates are
available for scheduling. With this limitation, the number of
decoding attempts is reduced to 15 (the grey areas are not decoded
in search for a control channel candidate), which corresponds to a
reduction by a factor of 3. In other words, there are four control
channel candidates in aggregation level 1, four control channel
candidates in aggregation level 2, four control channel candidates
in aggregation level 4, and three control channel candidates in
aggregation level 8.
With the above limitation put on the tree structure, scheduling
flexibility is not reduced that much, based on the following
arguments: If there is a lot of user equipments close to an eNB
scheduling the control channels, which user equipments require only
aggregation level 1, the aggregated level 2 elements with reduced
power can be used to have more users due to the possibility of
doing power balancing; in the example shown in FIG. 4, 9 favourable
conditioned users can be scheduled using this approach. In other
words, four control channels in aggregation level 1, two control
channels in aggregation level 2, two control channels in
aggregation level 4, and one control channel in aggregation level 8
can be scheduled. If a plurality of scheduled users is present at a
cell edge (aggregation level 8), additional users cannot be
scheduled anyway due to limited number of available control channel
elements. As the difference between aggregation layers is a factor
of 2 and when using power balancing, to some extent there is
flexibility to trade aggregation and power between each other.
It should be noted that although the above description is given for
an allocation tree for single link direction, the method is also
valid for the case where two trees, for uplink and downlink,
respectively, are present.
Further, it should be noted that the number of possible control
channels at each layer is not important.
According to an embodiment, using an allocation rule, usage of the
smallest control channel on all control channel elements is
prohibited, while at the same time the smaller control channels are
allowed to be combined to aggregated control channels with better
coverage.
With the above approach, the number of decoding attempts that is
needed by each UE can be reduced. The limitation of the tree is
possible due to the frequency diversity applied for all control
channel elements, such that each CCE experiences same or similar
channel conditions.
FIG. 5 shows a schematic block diagram illustrating a user
equipment 10 and a network device 20, such as an eNB, according to
an embodiment.
The user equipment 10 includes a receiving/transmitting section 11
and a decoding section 12. The receiving/transmitting section 11
receives symbols from the network device 20, which includes a
receiving transmitting section 21 transmitting the symbols and an
allocation section 22.
The allocation section 22 allocates control channels represented by
nodes of a tree structure, each of the control channels having at
least one control channel element carrying information for a
respective identifier used to detect a control channel of the
control channels, wherein the allocation is performed by limiting
allocation of highest level control channels of the control
channels, the highest level control channels being represented by
nodes of the tree structure at a highest level of the tree
structure. For example, in FIG. 1 the highest level is shown by
level 3. Referring to FIG. 4, the highest level is represented by
aggregation level 1.
The allocation section 22 may increase allocation of lower level
control channels of the control channels, the lower level control
channels being represented by nodes of the tree structure at lower
levels of the tree structure. For example, in FIG. 1 the lower
levels are shown by levels 2 and 1. Referring to FIG. 4, the lower
levels are represented by aggregation levels 2, 4 and 8.
The receiving/transmitting section 21 may transmit the allocated
control channels as symbols to user equipments including the user
equipment 10, by distributing the allocated control channels to
sub-carriers over a system bandwidth.
The higher level control channels may be combined to the lower
level control channels. In other words, smaller control channels
are allowed to be combined to aggregated control channels with
better coverage.
The allocation section 22 may increase allocation more the lower
the level of the tree structure.
The searching section 12 of the user equipment 10 searches for a
control channel by decoding control channels represented by nodes
of a tree structure, by using an identifier such as an MAC ID, CRC
or c-RNTI, each of the control channels having at least one control
channel element carrying information for a respective identifier
used to detect a control channel of the control channels, wherein
the searching section 12 limits the searching for highest level
control channels of the control channels, the highest level control
channels being represented by nodes of the tree structure at a
highest level of the tree structure.
The searching section 12 may increase the searching for lower level
control channels of the control channels, the lower level control
channels being represented by nodes of the tree structure at lower
levels of the tree structure.
The receiving/transmitting section 11 may receive the control
channels as symbols from the network device 20.
The searching section 11 may begin the searching with lowest level
control channels represented by nodes of the tree structure at a
lowest level of the tree structure. For example, in FIG. 1 the
lowest level is shown by level 1. Referring to FIG. 4, the lowest
level is represented by aggregation level 8.
It is to be noted that the network device 20 and user equipment 10
shown in FIG. 5 may have further functionality for working e.g. as
eNodeB and UE. Here the functions of the network device and user
equipment relevant for understanding the principles are described
using functional blocks as shown in FIG. 5. The arrangement of the
functional blocks of the network device and user equipment is not
construed to limit the invention, and the functions may be
performed by one block or further split into sub-blocks.
According to an embodiment, on a transmitting side, control
channels represented by nodes of a tree structure are allocated,
each of the control channels having at least one control channel
element carrying information for a respective identifier used to
detect a control channel of the control channels. The allocation is
performed by limiting allocation of highest level control channels
of the control channels, the highest level control channels being
represented by nodes of the tree structure at a highest level of
the tree structure. On a receiving side, a control channel is
searched for by decoding the allocated control channels, wherein
the searching is limited for the highest level control
channels.
The system also includes permanent or removable storage, such as
magnetic and optical discs, RAM, ROM, etc. on which the process and
data structures of the present invention can be stored and
distributed. The processes can also be distributed via, for
example, downloading over a network such as the Internet. The
system can output the results to a display device, printer, readily
accessible memory or another computer on a network.
It is to be understood that the above description is illustrative
of the invention and is not to be construed as limiting the
invention. Various modifications and applications may occur to
those skilled in the art without departing from the scope of the
invention as defined by the appended claims which may include the
phrase "at least one of A, B and C" as an alternative expression
that means one or more of A, B and C may be used, contrary to the
holding in Superguide v. DIRECTV, 358 F3d 870, 69 USPQ2d 1865 (Fed.
Cir. 2004).
* * * * *