Including Feedback Information Regarding
An Individual Subband Of A Wireless Channel
Background
[0001 ] Various wireless access technologies have been proposed or implemented to
enable mobile stations to perform communications with other mobile stations or with wired
terminals coupled to wired networks. Examples of wireless access technologies include
GSM (Global System for Mobile communications) and UMTS (Universal Mobile
Telecommunications System) technologies, defined by the Third Generation Partnership
Project (3GPP); and CDMA 2000 (Code Division Multiple Access 2000) technologies,
defined by 3GPP2.
[0002] As part of the continuing evolution of wireless access technologies to improve
spectral efficiency, to improve services, to lower costs, and so forth, new standards have been
proposed. One such new standard is the Long Term Evolution (LTE) standard from 3GPP,
which seeks to enhance the UMTS wireless network.
[0003] In some cases, it may be desirable to provide feedback information regarding a
wireless channel, where the feedback information can be sent from a mobile station to a base
station. The feedback information can include information to allow the base station to apply
a selected modulation and coding to data sent from the base station to the mobile station. In
addition, the feedback information can include an indication of a quality of a wireless
channel.
[0004] According to a conventional LTE standard, a wireless channel for
communicating data is divided into subbands (also referred to as bands). A subset of
subbands can be identified as optimal subbands that can be used for communication of data
between the base station and the mobile station. The conventional LTE standard supports
multiple modes of information feedback, but they may not be optimal. For example, PUSCH
(physical uplink shared channel) reporting Mode 2-2 as defined by the LTE standard does not
allow for feedback information regarding the wireless channel to be provided on an
individual subband basis for the selected subbands, which can reduce flexibility and reduce
the quality of data communications over the wireless channel.

Summary
[0005] In general, according to a preferred embodiment, to report feedback information
regarding a wireless channel, a mobile station determines whether a predefined condition is
satisfied. If so, feedback information regarding an individual one of plural subbands of the
wireless channel is included in a report to be sent to a base station. However, in response to
determining that the predefined condition is not satisfied, aggregate feedback information
regarding the plural subbands is included in another report to be sent to the base station.
[0006] Other or alternative features will become apparent from the following
description, from the drawings, and from the claims.
Brief Description Of The Drawings
[0007] Fig. 1 is a block diagram of an exemplary arrangement that includes a wireless
communications network that incorporates a preferred embodiment of the invention;
[0008] Figs. 2 and 3 illustrate different reports that can be communicated from a mobile
station to a base station to provide feedback information regarding a wireless channel,
according to a preferred embodiment; and
[0009] Figs. 4-8 are flow diagrams of processes of communicating and/or using
feedback information regarding a wireless channel, according to preferred embodiments.
DETAILED DESCRIPTION
[0010] In the following description, numerous details are set forth to provide an
understanding of some embodiments. However, it will be understood by those skilled in the
art that some embodiments may be practiced without these details and that numerous
variations or modifications from the described embodiments may be possible.

[0011] In accordance with some preferred embodiments, a technique or mechanism for
reporting feedback information regarding a wireless channel is provided, in which feedback
information regarding individual subbands can be provided to a base station. As used here,
the term "wireless channel" refers to a collection of resources that can be used by wireless
nodes, including mobile stations and base stations, to communicate wirelessly with each
other. The resources include subcarriers of different frequencies. In addition, resources can
include different time slots or different precoding vectors. In one embodiment, a wireless
channel can be implemented according to an orthogonal frequency division multiplexing
(OFDM) arrangement in which resources of the wireless channel are defined by combinations
of time slots (along a time dimension) and subcarriers of different frequencies (along a
frequency dimension).
[0012] In the OFDM arrangement, a subband (also referred to as "band") can include a
number of subcarriers along the frequency dimension and all the OFDM symbols (time slots)
along the time dimension. A wireless channel can thus be divided into multiple subbands.
More generally, a "subband" refers to some predefined portion of a wireless channel, which
can have multiple such predefined portions to use for communicating data between mobile
stations and base stations.
[0013] The feedback information that can be provided from the mobile station to the
base station includes feedback information to recommend modulation and coding to be
applied by the base station on downlink signaling (traffic data and/or control signaling and/or
reference signaling) transmitted by the base station to the mobile station. In this case, the
feedback information includes an index (or other type of indicator) to enable selection of
modulation and coding to be applied to signaling on the downlink. In some examples, this
index includes a precoding matrix index (PMI) that can be used to apply precoding at the
base station.
[0014] Another example of feedback information that can be sent from a mobile station
to a base station includes a channel quality indicator (CQI), which is an indication of wireless
channel quality.
[0015 ] In accordance with some embodiments, the type of feedback information that is
reported from the mobile station back to the base station depends on whether a predefined

condition is satisfied. In some implementations, this predefined condition is an indication of
whether or not the mobile station is a slow moving (or stationary) mobile station or a fast
moving (high velocity) mobile station. For a slow moving mobile station, it is likely that
parameters of the feedback information do not change over several reporting periods, such
that reporting the same parameters in corresponding reporting periods is redundant. For a
slow moving mobile station, instead of repeatedly sending the same parameters in successive
reporting periods, different feedback information can be sent in the different reporting
periods. In other words, the reporting periodicity of different types of feedback information
for different users can be set to different values.
[0016] In some reporting modes, the feedback information (including CQI and/or PMI)
that is sent from the mobile station to the base station is an aggregate feedback information
that reflects the properties of multiple subbands. The aggregate feedback information can be
information that reflects an average or some other aggregate of properties of multiple
subbands.
[0017] However, in accordance with some preferred embodiments, when the predefined
condition is detected, instead of sending aggregate feedback information, individual feedback
information for individual subbands can be reported (referred to as "incremental feedback
reporting"). Thus, for example, instead of reporting an aggregate CQI for multiple subbands,
an individual CQI for an individual subband can be reported. Similarly, instead of reporting
an aggregate PMI that is based on aggregate properties of multiple subbands, an individual
PMI can be reported for an individual subband.
[0018] From among a collection of subbands of a wireless channel, a subset of the
subbands can be identified as being the preferred or "best" subbands of the wireless channel.
For example, M (M > 1) subbands can be identified. These M subbands can be used for
communicating traffic data or higher-layer signaling information between a base station and a
mobile station.
[0019] Fig. 1 shows an exemplary wireless network in which some embodiments of the
invention can be provided. The wireless network includes a base station 100 that includes an
antenna array or other assembly (multi-beam antenna) 102 for sending wireless signals along
multiple paths 104,106 (spatial beams) in a corresponding cell sector 108. In a different

implementation, the antenna array 102 can include just a single antenna for sending wireless
signals along one path.
[0020] A cell sector is one section of a cell of a cellular network. Although just two
paths 104 and 106 are depicted in Fig. 1, it is noted that more than two paths (or just one
path) can be provided in a cell sector in other embodiments. In alternative implementations,
rather than providing multiple beams in a cell sector, it is noted that multiple beams can be
provided in a cell. As used here, the term "cell segment" can refer to either a cell sector or a
cell.
[0021 ] Although just one base station is depicted in Fig. 1, it is noted that a wireless
network would typically include multiple base stations. In some embodiments, the wireless
network is an LTE wireless network. In alternative embodiments, other types of wireless
networks can be employed. Note that reference to a "LTE wireless network" refers to a
wireless network that conforms to the requirements of the LTE standard developed by 3GPP,
as that standard is modified or evolved over time, as well as to subsequent standards that
evolve from LTE. Moreover, even though reference is made to LTE wireless networks in the
ensuing discussion, it is noted that techniques according to preferred embodiments can also
be applied to non-LTE, OFDM-based wireless networks.
[0022] In an LTE wireless network, the base station 100 includes an enhanced node B
("eNode B"), which includes a base transceiver station that includes the antenna array 102.
The base station 100 may also includes a radio network controller that cooperates with the
enhanced node B. The radio network controller and/or enhanced node B can perform one or
more of the following tasks: radio resource management, mobility management for managing
mobility of mobile stations, routing of traffic, and so forth. Note that one radio network
controller can access multiple eNode Bs, or alternatively, an eNode B can be accessed by
more than one radio access controller.
[0023] More generally, the term "base station" can refer to a cellular network base
station, an access point used in any type of wireless network, or any type of wireless
transmitter to communicate with mobile stations.

[0024] As depicted in Fig. 1, the base station 100 includes one or more central
processing units (CPUs) 122, which is (are) connected to storage 124. Moreover, the base
station 100 includes software 126 that is executable on the CPU(s) 122 to perform tasks of
the base station 100, including tasks according to preferred embodiments to enable support
for SDMA in the LTE wireless network.
[0025] The mobile station 110 of Fig. 1 also includes one or more CPUs 130 that are
connected to storage 132. The mobile station 110 also includes software 134 that is
executable on the CPU(s) 130 to perform tasks of the mobile station 110.'
[0026] The base station 100 is connected to a serving and/or packet data network
(PDN) gateway 112, which terminates the user plane interface toward the enhanced node B
and assumes the responsibility for packet routing and transfer towards an external network
114, which can be a packet data network such as the Internet or other type of network.
[0027] The arrangement depicted in Fig. 1 is provided for purposes of example. In other
implementations, other wireless network arrangements are used.
[0028] As noted above, in accordance with some embodiments, incremental reporting
of feedback information including CQI and PMI can be performed. In one implementation,
the reporting of such feedback information can be in the physical uplink shared channel
(PUSCH). However, in other implementations, feedback information can be provided in
other types of channels or messages sent from the mobile station to the base station, e.g., the
physical uplink control channel (PUCCH). Generally, feedback information is referred to as
being sent in a report, where a "report" can include a message, fields of a message, multiple
messages, and so forth.
[0029] According to some implementations, two modes of operation as defined by the
LTE standards can employ the incremental feedback reporting according to preferred
embodiments. These two modes of operation include LTE PUSCH reporting Mode 2-0 and
Mode 2-2. PUSCH reporting Mode 2-0 as defined by LTE is used for single input, multiple
output (SIMO) communication, spatial frequency block coding (SFBC) communication, or
open-loop spatial multiplexing (SM) communication. In this reporting mode, the precoding
information is not included in the feedback.

[0030] Mode 2-2 according to LTE refers to closed loop MIMO (multiple input,
multiple output) communication, where closed-loop MIMO uses feedback information to
apply coding. For example, based on feedback information (in the form of a PMI) from the
mobile station, the base station applies a selected precoding.
[0031 ] Although reference is made to LTE Mode 2-0 and Mode 2-2 in this discussion,
it is noted that incremental feedback reporting according to preferred embodiments can also
be applied to other types of wireless communications.
[0032] Incremental reporting of individual CQIs is depicted in Fig. 2 for an enhanced
LTE PUSCH reporting Mode 2-0. Four reports are depicted in Fig. 2 for four successive
reporting time intervals (1,2, 3,4). In one implementation, these four reports are carried by
PUSCH from the mobile station to the base station. The report that is sent from the mobile
station to the base station includes a bitmap field 202 that contains a bitmap, a subband CQI
information field 204 that selectively contains an aggregate CQI or individual CQI, and a
wideband CQI information field 206 that contains a wideband CQI. The bitmap identifies the
M preferred subbands. The bitmap includes a number of bits that correspond to respective
subbands. Setting a respective one of the bits means that a corresponding subband is
identified as preferred. In other implementations, other types of data structures can be used
to indicate which subbands are preferred.
[0033] The subband CQI information field 204 can either include an aggregate CQI for
the M subbands identified by the bitmap, or an individual CQI for one of the M subbands. In
reporting time interval 1, as shown in Fig. 2, the subband CQI information field 204 contains
an aggregate CQI over the M subbands. The wideband CQI information field 206 contains
the aggregate CQI over the entire wireless channel including all the subbands.
[0034] It is assumed that in reporting interval 1, the predefined condition discussed
above is not satisfied, such that the CQI that is communicated in the subband CQI
information field 204 is an aggregate CQI over the M subbands. In some embodiments, the
predefined condition is based on the content of the bitmap. If the current bitmap is the same
as a prior bitmap (in a prior reporting interval), then the predefined condition is satisfied.
However, if the current bitmap is different from a prior bitmap in a prior reporting interval,
then the predefined condition is not satisfied. The bitmap staying the same in successive

reporting intervals is an indication that the mobile station is a slow moving or stationary
mobile station.
[0035] In the example of Fig. 2, it is assumed that in each of the reporting intervals 2-4,
the bitmap remains the same as the bitmap reported in time interval 1. In reporting interval 2,
the subband CQI information field 204 includes the individual CQI for a first individual
subband from among the M subbands. Similarly, in reporting intervals 3 and 4, the subband
CQI information fields 204 of the respective reports contain individual CQIs for
corresponding second and third subbands from the M subbands. Thus, when the bitmap does
not change, individual CQIs can be reported rather than the aggregate CQI.
[0036] Although Fig. 2 shows an implementation in which just one individual CQI for a
corresponding individual subband can be included in each report, it is noted that in alternative
implementations multiple individual CQIs for corresponding subbands can be included in one
report.
[0037] Fig. 3 shows reports sent in four different reporting intervals (1, 2, 3,4) for an
enhanced LTE PUSCH reporting Mode 2-2. In Mode 2-2, in addition to CQI information,
PMI information is also provided (since closed loop MIMO is used). Moreover, in Mode 2-2,
it is assumed that there are two transmitting codewords such that CQI information for the two
transmitting codewords are reported separately. In each report shown in Fig. 3, a bitmap field
302 contains the bitmap, a first subband CQI field 304 contains the subband CQI information
for a first transmitting codeword, a wideband CQI field 306 contains the wideband CQI, a
second subband CQI information field 308 contains the subband CQI information for a
second transmitting codeword, and a PMI information field 310 contains PMI information.
In the reporting interval 1 of Fig. 3, it is assumed that the current bitmap is different from the
prior bitmap (in the prior reporting interval). As a result, the subband CQIs provided in the
subband CQI information fields 304 and 308, as well as the PMI information in the PMI
information field 310, are aggregate CQIs and PMI, respectively, for the M subbands
identified by the bitmap in the field 302.
[0038] However, in reporting intervals 2-4, it is assumed that the bitmap stays the same
as the bitmap in reporting interval 1, in which case the subband CQI information fields 304

and 308 can include individual CQIs for corresponding transmitting codewords, with
different individual CQIs for different subbands reported in successive reporting intervals.
[0039] Also, in reporting time intervals 2-4, the PMI information contained in the PMI
information field 310 includes the individual PMI for an individual subband, with different
individual PMIs reported for corresponding subbands in successive reporting time intervals
2-4.
[0040] Figs. 4 and 5 depict operations of a mobile station and base station, respectively,
for an enhanced PUSCH reporting Mode 2-0 operation. In a current reporting interval, the
mobile station determines (at 402) if the present bitmap is the same as the prior bitmap. If
not, the CQI information reported (at 404) in the subband CQI information field 204 (Fig. 2)
is the aggregate CQI over the M subbands. However, if the current bitmap is the same as the
prior bitmap, then the CQI information reported (at 406) in the subband CQI information
field 204 is the individual CQI for a corresponding individual subband.
[0041] As shown in Fig. 5, the base station determines (at 502) if the present bitmap is
the same as the prior bitmap. If not, then the base station uses (at 504) the aggregate CQI that
was previously received. However, if the current bitmap is the same as the prior bitmap, then
the base station uses (at 506) the individual CQI for a selected subband that is used for
transmission of downlink data from the base station to the mobile station.
[0042] Figs. 6 and 7 depict the enhanced PUSCH reporting Mode 2-2 operation of the
mobile station and base station, respectively. In Fig. 6, the mobile station determines (at 602)
if the present bitmap is the same as the prior bitmap. If not, then the subband CQI
information fields 304 and 308 and the PMI information field 310 (Fig. 3) of the feedback
report are provided (at 604) with aggregate CQI and PMI information for the M subbands.
However, if the current bitmap is the same as the prior bitmap, then individual CQIs and an
individual PMI are provided (at 606) in corresponding fields 304, 308, and 310 as depicted in
time interval 2, 3, or 4 of Fig. 3.
[0043] Fig. 7 illustrates the operation of the base station. The base station determines
(at 702) if the current bitmap is the same as the prior bitmap. If not, the base station uses (at
704) the aggregate CQIs and aggregate PMI for transmitting downlink information to the

mobile station. On the other hand, if the current bitmap is the same as the prior bitmap, then
the base station uses (at 706) the corresponding individual CQIs and individual PMI for the
selected subband that is used by the base station for communicating data to the mobile
station.
[0044] In the foregoing discussion, it is assumed that the mobile station makes the
decision regarding whether incremental reporting of individual CQIs and/or PMIs for
subbands is to be performed. In an alternative embodiment, it is the base station that makes
the decision regarding whether or not the mobile station should send individual feedback
information for individual subbands.
[0045] For example, as shown in Fig. 8, the base station can decide that the base station
wishes to receive individual feedback information about individual subbands from the mobile
station. In response to making such a decision, the base station sends (at 802) a control
indication to the mobile station. The control indication can be in the form of a higher layer
control signaling, such as Radio Resource Control (RRC) signaling, for example. The control
indication can be sent in response to the base station determining that a predefined condition
is satisfied, such as the bitmap not changing in successive reporting intervals.
[0046] In response to the control indication, the mobile station sends (at 804) individual
feedback information (individual CQI(s) and/or individual PMI(s)) for individual subband(s)
to the base station. The individual feedback information can be communicated in a physical
uplink control channel (PUCCH) or other channel.
[0047] However, if the base station determines that the predefined condition is not
satisfied, then the base station sends another control indication to cause the mobile station to
send aggregate feedback information for plural subbands.
[0048] The tasks of Figs. 4-8 can be performed by software in the mobile station 110 or
base station 100 of Fig. 1. Instructions of such software are executed on a processor (e.g.,
CPUs 130 and 122 in Fig. 1). The processor includes microprocessors, microcontrollers,
processor modules or subsystems (including one or more microprocessors or
microcontrollers), or other control or computing devices. A "processor" can refer to a single
component or to plural components (e.g., one or multiple CPUs).

[0049] Data and instructions (of the software) are stored in respective storage devices,
which are implemented as one or more computer-readable or computer-usable storage media.
The storage media include different forms of memory including semiconductor memory
devices such as dynamic or static random access memories (DRAMs or SRAMs), erasable
and programmable read-only memories (EPROMs), electrically erasable and programmable
read-only memories (EEPROMs) and flash memories; magnetic disks such as fixed, floppy
and removable disks; other magnetic media including tape; and optical media such as
compact disks (CDs) or digital video disks (DVDs).
[0050] In the foregoing description, numerous details are set forth to provide an
understanding of the present invention. However, it will be understood by those skilled in the
art that the present invention may be practiced without these details. While the invention has
been disclosed with respect to a limited number of embodiments, those skilled in the art will
appreciate numerous modifications and variations therefrom. It is intended that the appended
claims cover such modifications and variations as fall within the true spirit and scope of the
invention.

What is claimed is:
1. A method of reporting feedback information regarding a wireless channel comprising:
determining, by a mobile station, whether a predefined condition is satisfied;
in response to deteirnining that the predefined condition is satisfied, including, in a
first report to be sent to a base station, feedback information regarding an individual one of
plural subbands of the wireless channel; and
in response to determining that the predefined condition is not satisfied, including, in
a second report to be sent to the base station, aggregate feedback information regarding the
plural subbands.
2. The method of claim 1, wherein determining whether the predefined condition is
satisfied comprises determining if a data structure identifying preferred subbands has
changed.
3. The method of claim 2, wherein determining if the data structure identifying preferred
subbands has changed comprises determining if a bitmap identifying the preferred subbands
has changed.
4. The method of claim 1, further comprising:
after sending the first report, including, in a third report to be sent to the base station,
further feedback information regarding a second individual one of the plural subbands if the
predefined condition is satisfied.
5. The method of claim 1, further comprising:
including in the first report further feedback information regarding a second
individual one of the plural subbands.
6. The method of claim 1, further comprising:
performing, by the mobile station, data communication using one or more of the
plural subbands that are less than all available subbands of the wireless channel.

7. The method of claim 6, wherein performing the data communications is according to
Long Term Evolution (LTE) PUSCH (physical uplink shared channel) Mode 2-0.
8. The method of claim 6, wherein performing the data communications is according to
Long Term Evolution (LTE) PUSCH (physical uplink shared channel) Mode 2-2.
9. The method of claim 6, wherein performing the data communication is according to a
closed loop MIMO (multiple input, multiple output) mode of operation.
10. The method of claim 9, wherein the mobile station is to transmit plural codewords,
and wherein the feedback information included in the first report is for a first of the plural
codewords, and wherein the first report further includes feedback information for an
individual subband for another one of the plural codewords.
11. The method of claim 1, wherein the feedback information in the first report for the
individual subband comprises one of a precoding matrix index (PMI) and channel quality
indicator (CQI).
12. A base station comprising:
an interface to communicate wirelessly over a wireless channel with a mobile station;
and
a processor to:
determine if a condition is satisfied;
in response to determining that the condition is satisfied, using individual
feedback information for an individual subband of plural subbands of the wireless channel;
and
in response to determining that the condition is not satisfied, using aggregate
feedback information for the plural subbands.
13. The base station of claim 12, wherein the individual feedback information or
aggregate feedback information is used for downlink signaling and traffic data to be sent to
the mobile station.

14. The base station of claim 12, wherein the individual feedback information comprises
an individual channel quality indicator (CQI).
15. The base station of claim 12, wherein the individual feedback information comprises
an individual precoding matrix index (PMI).
16. The base station of claim 12, wherein the condition is satisfied if a bitmap for a
current reporting interval is unchanged from a bitmap for a prior reporting interval, wherein
the bitmap identifies the plural subbands.
17. A mobile station comprising:
an interface to communicate wirelessly over a wireless channel with a base station;
and
a processor to:
determine whether a predefined condition is satisfied;
in response to determining that the predefined condition is satisfied, include,
in a first report to be sent to a base station, individual feedback information regarding an
individual one of plural subbands of the wireless channel; and
in response to determining that the predefined condition is not satisfied,
including, in a second report to be sent to the base station, aggregate feedback information
regarding the plural subbands.
18. The mobile station of claim 17, wherein the first report includes a bitmap identifying
the plural subbands as being preferred subbands.
19. The mobile station of claim 17, wherein the individual feedback information includes
one of an individual channel quality indicator (CQI) and an individual precoding matrix
index (PMI).
20. The mobile station of claim 17, wherein the predefined condition is satisfied if a
bitmap identifying the plural subbands remains the same in successive reporting intervals.

21. A base station comprising:
an interface to communicate wirelessly over a wireless channel with a mobile station;
and
a processor to:
send a control indication to the mobile station to cause the mobile station to
send individual feedback information regarding at least one individual subband of plural
subbands of a wireless channel; and
receive at least one message from the mobile station containing the individual
feedback information that is responsive to the control indication.
22. The base station of claim 21, wherein the plural subbands are preferred subbands
selected from among all subbands of the wireless channel.
23. The base station of claim 21, wherein sending the control indication is in response to
determining that a predefined condition is satisfied, the method further comprising:
in response to determining that the predefined condition is not satisfied, send another
control indication to the mobile station to cause the mobile station to send aggregate feedback
information for the plural subbands.
24. A mobile station comprising:
an interface to communicate wirelessly over a wireless channel with a base station;
and
a processor to:
receive a control indication from the base station to indicate that individual
feedback information regarding at least one individual subband of plural subbands of a
wireless channel is to be sent; and
in response to the control indication, send at least one message to the base
station containing the individual feedback information.

25. The mobile station of claim 24, wherein the control indication is received in response
to the base station determining that a predefined condition is satisfied, the method further
comprising:
receiving another control indication from the base station to cause the mobile station
to send aggregate feedback information for the plural subbands, wherein the another control
indication is in response to the base station determining that the predefined condition is not
satisfied.

To report feedback information
regarding a wireless channel, a
mobile station determines whether a predefined
condition is satisfied. In response
to determining that the predefined
condition is satisfied, feedback information
regarding an individual one of
plural subbands of the wireless channel
is included in a first report to be sent to
a base station. In response to determining
that the predefined condition is not
satisfied, aggregate feedback information
regarding the plural subbands is included
in a second report to be sent to
the base station.