U.S. patent application number 11/859148 was filed with the patent office on 2008-02-28 for base station and method for selecting best transmit antenna(s) for signaling control channel information.
Invention is credited to David Astely, Karl James Molnar, Tomas Sundin.
Application Number | 20080051037 11/859148 |
Document ID | / |
Family ID | 39737094 |
Filed Date | 2008-02-28 |
United States Patent
Application |
20080051037 |
Kind Code |
A1 |
Molnar; Karl James ; et
al. |
February 28, 2008 |
BASE STATION AND METHOD FOR SELECTING BEST TRANSMIT ANTENNA(s) FOR
SIGNALING CONTROL CHANNEL INFORMATION
Abstract
A base station is described herein which implements a method
that uses different aspects of reported channel quality information
(CQI) measurements to help select the "best" transmit antenna(s) on
which to transmit control channel information to mobile
terminal(s). The base station can also transmit a format indicator
to communicate the assigned control channel transmit antenna(s) and
the assigned data transmit antenna(s) to the mobile
terminal(s).
Inventors: |
Molnar; Karl James; (Cary,
NC) ; Sundin; Tomas; (Stockholm, SE) ; Astely;
David; (Bromma, SE) |
Correspondence
Address: |
ERICSSON INC.
6300 LEGACY DRIVE
M/S EVR 1-C-11
PLANO
TX
75024
US
|
Family ID: |
39737094 |
Appl. No.: |
11/859148 |
Filed: |
September 21, 2007 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11275388 |
Dec 29, 2005 |
|
|
|
11859148 |
Sep 21, 2007 |
|
|
|
Current U.S.
Class: |
455/70 |
Current CPC
Class: |
H04B 7/0632 20130101;
H04W 72/1278 20130101; H04B 7/061 20130101; H04B 17/309 20150115;
H04B 7/0413 20130101; H04B 7/0691 20130101 |
Class at
Publication: |
455/070 |
International
Class: |
H04B 7/005 20060101
H04B007/005 |
Claims
1. A method for selecting one or more transmit antennas from which
to transmit control channel information to one or more receivers,
said method comprising the steps of: receiving channel quality
information measurements from the one or more receivers; and
analyzing the received channel quality information measurements to
select which transmit antenna(s) to use for transmitting the
control channel information to the one or more receivers.
2. The method of claim 1, further comprising the step of
transmitting a format indicator to the one or more receivers where
the format indicator identifies the transmit antenna assignments
for both data information and the control channel information.
3. The method of claim 1, wherein when said received channel
quality information measurements have a specific antenna detection
ordering then said analyzing step results in selecting the transmit
antenna(s) which are going to be detected first by the one or more
receivers.
4. The method of claim 1, wherein when said received channel
quality information measurements have a value for each sub-band
within a signal bandwidth for each transmit antenna then said
analyzing step includes a step of restricting the selection of
possible transmit antenna(s) that could be used to transmit the
control data information to be from a group of transmit antenna(s)
which had been selected to transmit data to the one or more
receivers.
5. The method of claim 4, wherein said restricting step further
includes a step of using a sum data rate over each sub-band within
the signal bandwidth for each transmit antenna that is used for
data transmission when determining the transmit antenna(s) which
are to be used to transmit the control data information to the one
or more receivers.
6. The method of claim 4, wherein said restricting step further
includes a step of restricting the sub-band(s) within the signal
bandwidth for each transmit antenna that could be used to transmit
the control data information to the one or more receivers.
7. The method of claim 1, wherein when said received channel
quality information measurements have a specific antenna detection
ordering and a value corresponding to each sub-band within a signal
bandwidth for each transmit antenna then said analyzing step
includes a step of computing a sum data rate for each potential
transmit antenna and a step of assigning the control data
information to the transmit antenna(s) which are going to be
detected first by the one or more receivers.
8. The method of claim 1, wherein when the control channel
information is transmitted to multiple receivers then said
analyzing step includes a step of selecting the transmit antenna(s)
which satisfy the most disadvantaged receiver of the multiple
receivers.
9. The method of claim 1, further comprising a step of transmitting
a format indicator to the one or more receivers where the format
indicator identifies a first transmit antenna assignment for the
control channel information and a first detected transmit antenna
of the data channel and a second transmit antenna assignment for
the remaining detected antennas of the data channel.
10. The method of claim 9, further comprising the step of
transmitting the portion of the format indicator that identifies a
first transmit antenna assignment for the control channel
information and the first detected transmit antenna to the one or
more receivers on a first transmission and transmitting the portion
of the format indicator that identifies the second transmit antenna
assignment for the remaining detected antennas of the data channel
on a second transmission to the one or more receivers.
11. A base station comprising: a user scheduling unit that receives
channel quality information measurements and outputs user
scheduling information and control channel information; a control
channel antenna mapping unit that receives the channel quality
information measurements and the user scheduling information and
processes the channel quality information measurements and the user
scheduling information to select which transmit antenna(s) should
be used to transmit the control channel information; and an antenna
switch that receives a transmit antenna selection from said control
channel antenna mapping unit and the control channel information
from said user scheduling unit and then uses the selected transmit
antenna(s) to transmit the control channel information.
12. The base station of claim 11, wherein said control channel
antenna mapping unit specifies a format indicator to indicate
transmit antenna assignments for both data information and the
control channel information.
13. The base station of claim 11, wherein when said received
channel quality information measurements have a specific ordering
then said control channel antenna mapping unit selects the transmit
antenna which is first detected by a receiver.
14. The base station of claim 11 wherein when said received channel
quality information measurements have no specific ordering then
said control channel antenna mapping unit selects the transmit
antenna(s) which have a highest individual data rate(s) from a
group of transmit antenna(s) that had been selected to transmit
data to a receiver.
15. The base station of claim 14, wherein when said received
channel quality information measurements have no specific ordering
then said control channel antenna mapping unit selects the transmit
antenna(s) which have a highest sum data rate(s) from a group of
transmit antenna(s) that had been selected to transmit data to a
receiver.
16. The base station of claim 11, wherein when the control channel
information is transmitted to multiple receivers then said control
channel antenna mapping unit selects the transmit antenna(s) which
satisfy the most disadvantaged receiver of the multiple
receivers.
17. The base station of claim 11, wherein said user scheduling
unit, said control channel antenna mapping unit and said antenna
switch are part of an orthogonal frequency division multiplexing
system.
18. A receiver comprising: a receiving unit that receives a format
indicator from a base station; and a processor that processes the
format indicator to determine which transmit antenna(s) in the base
station are going to transmit control data channel information and
which transmit antenna(s) in the base station are going to transmit
data information.
19. The receiver of claim 18, further comprising a transmitting
unit that transmits channel quality information measurements
associated with the transmit antennas in the base station where the
channel quality information measurements have a specific
ordering.
20. The receiver of claim 18, further comprising a transmitting
unit that transmits channel quality information measurements
associated with the transmit antennas in the base station where the
channel quality information measurements have a value corresponding
to each sub-band within a signal bandwidth for each transmit
antenna in the base station.
Description
CLAIMING BENEFIT OF PRIOR FILED U.S. APPLICATION
[0001] This application is a continuation-in-part application of
U.S. patent application Ser. No. 11/275,388, filed Dec. 29, 2005,
and entitled "MIMO Control Channel with Shared Channelization
Codes".
TECHNICAL FIELD
[0002] The present invention relates to the wireless communications
field, and in particular, to a base station and method for
selecting which transmit antenna(s) should be used to transmit
control channel information to one or more receivers (mobile
terminals).
BACKGROUND
[0003] The following abbreviations are herewith defined, at least
some of which are referred to within the ensuing description of the
prior art and the present invention.
CQI Channel Quality Information
HS-DSCH High-Speed Downlink Shared Channel
HS-SCCH High-Speed Shared Control Channel
LTE Long Term Evolution
Mbps Megabits Per Second
MCS Modulation and Coding Scheme
MIMO-SCCH Multiple Input Multiple Output Shared Control Channel
MMSE Minimum Mean-Square Estimation
OFDM Orthogonal Frequency Division Multiplexing
PARC Per-Antenna Rate Control
SNR Signal-Noise-Ratio
S-PARC Selective Per-Antenna Rate Control
SIC Successive Interference Cancellation
TTI Total Timeslot Interval
NCDMA Wideband CDMA
[0004] In the multi-antenna concept proposed for the HSDPA mode of
a WCDMA cellular system, the selection of a subset of antennas by
the base station from which to transmit data streams to mobile
terminals is considered an extension of fast link adaptation for
single-antenna systems. This multi-antenna approach leads to a
transmission antenna mode that is closely matched to the existing
propagation conditions between the base station and mobile
terminals. In one case, the base station can utilize PARC which is
a multi-antenna approach that provides high downlink data rates to
mobile terminals (see, S. J. Grant et al. "Per-Antenna-Rate-Control
(PARC) in Frequency Selective Fading with SIC-GRAKE Receiver" Los
Angeles, September 2004). In this approach, the base station uses
separate transmission rates for the data streams which are mapped
to all of the transmit antennas. In another case, the base station
can utilize S-PARC which is a multi-antenna approach that provides
even higher downlink data rates to the mobile terminals (see, S. J.
Grant et al. "System-Level Performance Gains of Selective
Per-Antenna-Rate-Control (S-PARC)" published in the IEEE Spring
Vehicular Technology Conference, May 2005). In this approach, the
base station selectively adapts both the transmit antenna(s) and
the transmission data rates which are to be used to transmit the
data streams to the mobile terminals.
[0005] As part of the fast link adaptation process, the mobile
terminals measure the CQI and transmit the CQI measurements on the
uplink to the base station so that the base station can use the CQI
measurements to select the transmission data rate assignment and if
needed the transmit antenna(s) assignment. Since the base station
transmits signals concurrently from different transmit antennas
these signals interfere with each other which means the estimated
CQI is going to change for each combination of transmit antennas.
Thus, the providing of CQI estimates for each transmit antenna
under each combination of transmit antenna(s) is going to utilize a
large amount of the available uplink resources when compared to
single-antenna transmission. Moreover, the type of receivers
employed in the mobile terminals may increase the number of CQI
values that may be fed back on the uplink to the base station. For
example, the mobile terminal may have a SIC receiver which places
an ordering on the transmit antenna(s) so that there will be a
separate CQI value for each permutation (rather than combination)
of the transmit antenna(s).
[0006] One approach that can be used to reduce the complexity of
the CQI feedback from a mobile terminal that uses a SIC receiver
and implements S-PARC was described in co-assigned U.S. patent
application Ser. No. 10/841,911 filed on May 7, 2004 and entitled
"Reduced CQI Feedback for MIMO HSDPA" (the contents of which are
hereby incorporated by reference herein). In this approach, the
base station that is considering transmission with one antenna will
select the transmit antenna that provides the best rate and use
that for a single-antenna transmission. In considering transmission
with two antennas, the base station constrains the two-antenna
subset to contain the best antenna previously found for the
single-antenna transmission and the transmit antenna with the
next-best rate. This scheme is repeated for the three-antenna
subset, the four-antenna subset etc . . . , and in general is
called the "subset property" when related to the transmit antenna
selection. Thus, an order is given to the transmit antennas so that
the first antenna has the greatest transmit rate while the last
antenna has the lowest transmit rate. This ordering of antennas
from lowest to greatest rates is the order that the SIC-receiver
processes the received signals. As a result, a large number of
antenna orderings can be avoided and the feedback on the uplink can
be reduced by constraining the antenna order and antenna subset
selection by using a CQI report with this subset property.
[0007] Moreover, if the base station acquires the CQI report based
on the subset property then it can use this scheme to help
determine the set of antennas which are to be used for
transmission. Thereafter, the base station signals to the mobile
terminal the number of antennas used for transmission and the
transport formats for the transmitted streams. Since, both the base
station and the mobile terminal know the ordering contained as part
of the CQI report, the actual transmit antennas used for the
transmission could be determined by the mobile terminal. This
notion of antenna ordering can also be used with mobile
terminals/receivers that do not require an ordered set of antennas
for detection. In this situation, the antenna ordering is used
solely for providing an efficient CQI reporting technique and
allows the base station to select the number of transmit antennas
and the corresponding rates for subsequent transmissions.
[0008] In WCDMA, release 5, the base station can use four HS-SCCHs
and different channelization codes to transmit the transport
information to as many as four different mobile terminals during a
single TTI. While, the co-pending U.S. patent application Ser. No.
11/275,388 introduced a MIMO shared control channel (MIMO-SCCH)
which the base station could use to signal the transport
information to a mobile terminal that is capable of receiving a
multi-stream transmission. In the HSDPA mode, the base station
reliably transmits the HS-SCCHs and MIMO-SCCH by using a spreading
code of 128 to ensure the strength of the despread signal. In
addition, the base station can place the HS-SCCHs and MIMO-SCCH on
the best transmit antenna to help improve the SNR of these control
channels. However, in a LTE mode which is based on OFDM there is no
such spreading code which can be used to boost the signal level of
one antenna relative to the other transmit antennas (note: WiMAX
and 4G systems are other types of OFDM systems). Thus, to help
ensure the reliable transmission of the shared control channel and
information thereon from one antenna to the mobile terminal(s), the
base station could use a couple of different approaches as follows:
[0009] For those OFDM symbols corresponding to the shared control
channel, allow no other antenna to transmit at the same symbol
positions. This, of course, denies use of the same OFDM tiles for
the transmission of data. [0010] The information on the shared
control channel can be encoded using a stronger code rate to
overcome interference from the other transmit antennas. However,
this may not be the most effective approach since the control
channel already has strong coding and this coding would be used to
overcome interference that has been self-generated. [0011] Use
interference cancellation techniques at the mobile terminal to
cancel the interfering signals from the other transmit antennas.
However, to cancel the self-interference generated by multiple
transmit antennas, the mobile terminal has to know which antennas
are used for data transmission and for the control channel so the
appropriate quantities (e.g. impairment covariance matrix) can be
constructed at the receiver. [0012] Transmit the control channel on
the "best" antenna. In the co-pending U.S. patent application Ser.
No. 11/275,388, the best antenna is the one with the highest SNR as
reported within the CQI measurements. However, when there are
multiple CQI measurements reported, for example, over different
sub-bands in an OFDM system, then this notion of best antenna is
ambiguous. Also, in co-pending U.S. patent application Ser. No.
11/275,388, the SNR associated with an antenna may be related to
the order the antennas are detected because it is generally desired
to have control channels detected prior to the data channels.
[0013] Thus, while it is clear that using the best transmit antenna
to advantageously transmit the control channel should be performed,
the decision about which antenna is best and the signaling required
to support this transmission needs further consideration. These
particular needs and other needs are satisfied by the base station
and method of the present invention.
SUMMARY
[0014] In one aspect, the present invention provides a base station
that includes: (a) a user scheduling unit that receives channel
quality information measurements (from a mobile terminal) and
outputs user scheduling information and control channel
information, (b) a control channel antenna mapping unit that
receives the channel quality information measurements (from the
mobile terminal) and the user scheduling information and processes
the channel quality information measurements and the user
scheduling information to select which transmit antenna(s) should
be used to transmit the control channel information; and (c) an
antenna switch that receives a transmit antenna selection from the
control channel antenna mapping unit and the control channel
information from the user scheduling unit and then uses the
selected transmit antenna(s) to transmit the control channel
information.
[0015] In yet another aspect, the present invention provides a
method for selecting one or more transmit antennas from which to
transmit control channel information to one or more receivers. The
method includes the steps of: (a) receiving channel quality
information measurements from the one or more receivers; and (b)
analyzing the received channel quality information measurements to
select which transmit antenna(s) to use for transmitting the
control channel information to the one or more receivers.
[0016] In still yet another aspect, the present invention provides
a receiver (mobile terminal) that includes: (a) a receiving unit
that receives a format indicator from a base station; and (b) a
processor that processes the format indicator to determine which
transmit antenna(s) in the base station are going to transmit
control data channel information and which transmit antenna(s) in
the base station are going to transmit data information.
[0017] Additional aspects of the invention will be set forth, in
part, in the detailed description, figures and any claims which
follow, and in part will be derived from the detailed description,
or can be learned by practice of the invention. It is to be
understood that both the foregoing general description and the
following detailed description are exemplary and explanatory only
and are not restrictive of the invention as disclosed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] A more complete understanding of the present invention may
be obtained by reference to the following detailed description when
taken in conjunction with the accompanying drawing:
[0019] FIG. 1 is a block diagram which is used to help explain how
a base station can take into account CQI measurements reported from
one or more mobile terminal(s) and determine which transmit
antenna(s) to use to transmit control channel information to the
one or more mobile terminal(s) in accordance with the present
invention.
DETAILED DESCRIPTION
[0020] Referring to FIG. 1, there is shown a block diagram that is
used to help explain how a base station 100 can take into account
various aspects of CQI measurements 103 received from one or more
mobile terminal(s) 106 to select which transmit antenna(s) 102
should be used to transmit control channel information 104 (via the
MIMO-SCCH) to the one or more mobile terminal(s) 106 in accordance
with the present invention. The base station 100 includes a user
scheduling unit 108, a control channel antenna mapping unit 110 and
an antenna switch 112 (note: only the components within the base
station 100 that are needed to help explain the present solution
have been discussed and illustrated herein). As shown, the user
scheduling unit 108 and the control channel antenna mapping unit
110 both receive CQI measurements 103 from the mobile terminal(s)
106. In this example, each CQI measurement 103 contains the channel
quality values for each transmit antenna 102 and each sub-band in
the downlink signal received by the corresponding mobile terminal
106. Upon receiving the CQI measurements 103, the user scheduling
unit 108 processes this information and outputs user scheduling
information 114 and control channel information 104. The control
channel antenna mapping unit 110 receives the COI measurements 103
and the user scheduling information 114 and then processes this
information to select which transmit antenna(s) 102 should be used
to transmit the control channel information 104 to the mobile
terminal(s) 106. Then, the control channel antenna mapping unit 110
outputs a transmit antenna selection 116 to the antenna switch 112.
The antenna switch 112 receives the transmit antenna selection 116
from the control channel antenna mapping unit 110 and the control
channel information 104 from the user scheduling unit 110 and then
uses the selected transmit antenna(s) 102 to transmit the control
channel information 104 to the mobile terminal(s) 106 (note: each
mobile terminal 106 can receive control channel information 104
from different transmit antenna(s) 102).
[0021] A detailed discussion about several different cases is
provided below to explain different ways the base station 100 can
select the "best" transmit antenna(s) 102 on which to assign the
control channel information 104 based on various assumptions
regarding the CQI feedback 103 which is received from the mobile
terminal(s) 106. While these different cases are discussed, it
should be noted that the first consideration should be whether the
mobile terminal 106 (receiver) assumes some implicit or explicit
ordering of the transmit antennas 102 and if there is ordering then
the antenna order is defined in a manner where signals assigned to
the selected antennas can be detected. In this case, it is desired
to place the control channel on the antennas first detected. If,
the mobile terminal 106 (receiver) does not require an antenna
detection order, even though the CQI reports may be ordered for
other purposes such as antenna selection, then it is still
desirable to place the control channel on the selected antenna 102
with the best CQI value. Plus, in the discussion below, it is
assumed that signals are mapped directly to transmit antennas 102.
However, the mapping between signals and antennas 102 may not need
to be mapped in such a direct manner which in effect creates a set
of virtual antennas (e.g. fixed beam-forming is one mapping that
forms a set of virtual antennas). As such, the present invention
also applies to the case of indirect mapping (i.e. virtual
antennas) as well as the direct mapping of signals to antennas.
[0022] In the first case, assume the CQI reports 103 have values
that are ordered and that the mobile terminals 106 (receivers) use
this antenna detection order. In this case, the CQI reports 103 may
use the subset property discussed above to reduce the amount of
feedback required in the uplink signaling. As discussed above, the
mobile terminal(s) 106 may submit ordered CQI reports 103 because
they have a SIC receiver 117. A simple example of an ordered CQI
report 103 for a 4-antenna S-PARC is illustrated in TABLE 1.
TABLE-US-00001 TABLE 1 Antenna MCS Rate (Mbps) A 4 B 2 C 1 D
0.05
[0023] TABLE 1 describes the set of antennas and the transmit rates
that the base station 100 can use for transmitting information to a
mobile terminal 106 in the following manner: for single-antenna
transmission then antenna A can be used with a transmit rate of 4
Mbps; two-antenna transmission uses antennas A and B with up to 6
Mbps: three antenna transmission uses antennas A, B, and C with a
rate of 7 Mbps, and transmission with all four antennas A, B, C and
D has a maximum rate of 7.05 Mbps (note: the reported CQI values
may be some metric other than rate (e.g. SNR levels) and if this is
the case then the rates could be derived from these metrics). When
the mobile terminal 106 uses SIC reception then the antenna with
the lowest rate is detected first where its signal is decoded,
re-encoded and subtracted from the composite received signal before
detecting the signal for the antenna with the next highest
rate.
[0024] Thus, for single-antenna transmission, the base station 100
should use antenna A for the shared control channel. Clearly, this
is more efficient than if the base station 100 placed the control
channel on antenna D. Next, consider when the base station 100
would use two transmit antennas A and B for data transmission.
Antenna A obtains its high rate since the signal from antenna B is
subtracted from the composite signal as part of the SIC process in
the mobile terminal 106. Therefore, it is preferable that the base
station 100 place the control channel signal on the first detected
antenna, namely antenna B. For three-antenna transmission, the base
station 100 would place the control channel signal on antenna C.
Finally, for four-antenna transmission, the base station 100 would
place the control channel signal on antenna D. Since, the number of
transmit antennas 102 and the antenna detection order is known to
the mobile terminal 106, the first detected antenna which contains
the control channel information 104 can be determined with little
additional signaling. In a situation where there is no antenna
detection ordering, then the base station 100 would determine the
best antenna to be the selected antenna with the highest rate. This
would be used even if the CQI report 103 is ordered for some other
purpose, such as for reducing the amount of information that would
need to be contained in the CQI report 103.
[0025] A second case arises when the mobile terminals 106 report
multiple CQI values for each transmit antenna 102, for example, in
an OFDM system the mobile terminals 106 would report CQI values 103
for each of the different sub-bands of the entire signal bandwidth
(see FIG. 1). In the following examples, consider an OFDM system
with four sub-bands and four transmitted streams (one per antenna
A, B. C and D). In this situation, a complete CQI report 103 has
four CQI rate values reported for each sub-band for each antenna A,
B, C and D. This exemplary CQI report 103 is shown in TABLE 2.
TABLE-US-00002 TABLE 2 Sub-band 1 Sub-band 2 Sub-band 3 Sub-band 4
Antenna (Mbps) (Mbps) (Mbps) (Mbps) A 1 3 2 3 B 2 1 3 4 C 4 2 1 2 D
3 4 4 1 Note: this exemplary CQI report 103 is used several times
hereinafter to help explain different aspects of the present
solution.
[0026] In TABLE 2, the mobile terminals 106 report the CQI
measurements 103 for the four antennas A, B, C and D for each
sub-band within the bandwidth of a received signal. Now, the base
station 100 needs to decide which antenna(s) A, B, C, or D should
be assigned to transmit the control channel information 104 to the
mobile terminals 106. A number of different possibilities exist and
depend on factors such as: (1) the assignment of mobile terminal(s)
106 to the different sub-bands; (2) the antenna selection for each
mobile terminal 106; and (3) the nature of the CQI report 103. Some
exemplary options are discussed in detail below:
[0027] A. The base station 100 can specify an antenna assignment
for the control channel information 104 for each sub-band in the
signal bandwidth depending on the antenna selection for data
transmission in each sub-band of the signal to the mobile terminals
106. In the above example, there would be four control channel
antenna assignments, one for each sub-band. As an example, if only
one antenna is selected for transmission in each sub-band, then the
antenna with the highest rate (those with the superscript.sup.1 in
TABLE 3) for each sub-band could be used for transmitting the
control channel information 104 to the mobile terminals 106. If two
antennas are selected in each sub-band, and a receiver-dependent
antenna order is specified for each sub-band, then the antennas
with the second highest rate (those with the superscript.sup.2 in
TABLE 3) for each sub-band could be used for transmitting the
control channel information 104 to the mobile terminals 106.
TABLE-US-00003 TABLE 3 Sub-band 1 Sub-band 2 Sub-band 3 Sub-band 4
Antenna (Mbps) (Mbps) (Mbps) (Mbps) A 1 .sup. 3.sup.2 2 .sup.
3.sup.2 B 2 1 .sup. 3.sup.2 .sup. 4.sup.1 C .sup. 4.sup.1 2 1 2 D
.sup. 3.sup.2 .sup. 4.sup.1 .sup. 4.sup.1 1
[0028] B. If the control channel is user-specific, meaning one
separately encoded control channel is assigned to each mobile
terminal 106, then the base station 100 could make the control
channel antenna assignment on a specific basis for each specific
mobile terminal 106. In this case, the base station 100 could make
the control channel antenna assignment as follows:
[0029] 1. The base station 100 can restrict the control channel
antenna assignment to the specific mobile terminal 106 to be one of
the antennas that had been selected for data transmission that is
in the sub-band(s) assigned to that user. For example, assume there
are two mobile terminals 106 where the base station 100 assigns one
mobile terminal 106 to sub-bands 2, 3 and 4 and uses antennas B and
D to transmit the control channel (see superscript.sup.1 in TABLE
4). Furthermore, the base station 100 assigns the other mobile
terminal 106 to the sub-band 1 and uses antenna C to transmit the
control channel (see superscript.sup.2 in TABLE 4). TABLE-US-00004
TABLE 4 Sub-band 1 Sub-band 2 Sub-band 3 Sub-band 4 Antenna (Mbps)
(Mbps) (Mbps) (Mbps) A 1 3 2 3 B 2 1 3 .sup. 4.sup.1 C .sup.
4.sup.2 2 1 2 D 3 .sup. 4.sup.1 .sup. 4.sup.1 1
[0030] 2. In addition to 1), the base station 100 can use the sum
rate over the sub-bands assigned for the user's data transmission
when determining which antenna to assign the control channel
information 104. In this case, the base station 100 rather than
assign antennas per sub-band, would assign only one antenna to be
used for the control channel across all of the assigned sub-bands.
Assuming a single antenna is used for data transmission, the base
station 100 could choose the antenna with the highest sum data rate
from which to send the control channel for each mobile terminal
106. In the same example above, the base station 100 would assign
one mobile terminal 106 to sub-bands 2, 3 and 4 and use antenna D
to transmit the control channel (see superscript.sup.1 in TABLE 5).
And, the base station 100 would assign the other mobile terminal
106 to sub-band 1 and use antenna C to transmit the control channel
(see superscript.sup.2 in TABLE 5). TABLE-US-00005 TABLE 5 Sub-band
1 Sub-band 2 Sub-band 3 Sub-band 4 Antenna (Mbps) (Mbps) (Mbps)
(Mbps) A 1 3 2 3 B 2 1 3 4 C .sup. 4.sup.2 2 1 2 D 3 .sup. 4.sup.1
.sup. 4.sup.1 .sup. 1.sup.1
[0031] 3. In addition to 1), the base station 100 can use the sum
rate over a set of select sub-bands to determine which antenna to
assign the control channel information 104 to each mobile terminal
106 (note: in this particular case the control channel would be
transmitted only in certain sub-bands). Using the same example
above except only the odd-numbered sub-bands are used, the base
station 100 would assign one mobile terminal 106 to sub-band 3 and
use antenna D to transmit the control channel (see
superscript.sup.1 in TABLE 6). And, the base station 100 would
assign the other mobile terminal 106 to the sub-band 1 and use
antenna C to transmit the control channel (see superscript.sup.2 in
TABLE 6). TABLE-US-00006 TABLE 6 Sub-band 1 Sub-band 2 Sub-band 3
Sub-band 4 Antenna (Mbps) (Mbps) (Mbps) (Mbps) A 1 3 2 3 B 2 1 3 4
C .sup. 4.sup.2 2 1 2 D 3 4 .sup. 4.sup.1 1
[0032] 4. In addition to 1), the base station 100 can after
computing the rate for each antenna, assign the control channel to
the first detected antenna in the case where there is a
receiver-dependent detection order specified by the respective
mobile terminal 106. TABLE 7 shows an example where two antennas
are used for data transmission in each sub-band and the sum rates
are computed for the mobile terminal 106 assigned to sub-bands 2-4
(using antennas A and D), and a second mobile terminal 106 assigned
to sub-band 1 (using antennas C and D). After computing the sum
rates, the base station 100 would transmit the control channel
information 104 on the first detected antenna A in sub-bands 2-4
(see superscript.sup.1) and on the first detected antenna D in
sub-band 1 (see superscript.sup.2). TABLE-US-00007 TABLE 7 Sub-band
1 Sub-band 2 Sub-band 3 Sub-band 4 Antenna (Mbps) (Mbps) (Mbps)
(Mbps) A 1 .sup. 3.sup.1 .sup. 2.sup.1 .sup. 3.sup.1 B 2 1 3 4 C 4
2 1 2 D .sup. 3.sup.2 4 4 1
[0033] In the situation, where the base station 100 transmits one
control channel that is shared among multiple mobile terminals 106,
then the above techniques could be used, however, the antenna
selection could also be made to satisfy the most disadvantaged
mobile terminal 106 out of all of the mobile terminals 106
designated for data transmission. For example, consider the case
associated with TABLE 4, where one mobile terminal 106 is assigned
to three sub-bands 2, 3 and 4 while the other mobile terminal 106
is assigned to only one sub-band 1. If the coding is accounted for,
then the mobile terminal 106 with the fewest possible bits to code
across would be disadvantaged with respect to the other mobile
terminal 106 that has more bits available for coding. Thus, the
disadvantaged mobile terminal 106 would be the one that was
assigned to sub-band 1 and as a result the base station 100 would
assign the control channel according to this particular mobile
terminal. Of course, the base station 100 should give some
consideration that the other mobile terminal 106 would not become
even more disadvantaged under this particular assignment.
[0034] In another aspect of the present solution, the base station
100 should have a way to signal the control channel antenna
assignment as well as which antennas were selected for data
transmission to the mobile terminal(s) 106. In the scenario, when
the base station 100 selects the transmitted antennas based on
antenna detection ordered CQI measurements 103, and the control
channel is placed on the first detected antenna according to that
antenna detection ordering, then all that is required for the base
station 100 to signal in the downlink is the number of transmitted
streams, since the ordering is already known at the corresponding
mobile terminal 106. Of course, if the mobile terminal 106 can not
derive the ordering, then the base station 100 would need to signal
this ordering to the mobile terminal 106. In another scenario, if
there is no such explicit or implicit ordering, then there is
ambiguity in which antennas are used by the base station 100 for
data transmission and control channel transmission to the mobile
terminal 106 and as a result the base station 100 needs to signal
this information to the corresponding mobile terminal 106.
[0035] If the control channel and data channel antenna assignments
are required to be signaled, then the base station 100 can signal
these two quantities together for a given transmission scheme to
the mobile terminal 106. For example, for a 4-antenna PARC
transmission scheme and when there is no assumed antenna detection
ordering at the mobile terminal 106 (e.g. when an MMSE receiver 117
is used), the base station 100 can signal a format indicator to the
mobile terminal 106 which is based on the following TABLE 8:
TABLE-US-00008 TABLE 8 Transmission Format Transmission Antenna
Indicator Type Mapping 1 PARC1a {1} 2 PARC1b {2} 3 PARC1c {3} 4
PARC1d {4} 5 PARC2a {1, 2} 6 PARC2b {1, 3} 7 PARC2c {1, 4} 8 PARC2d
{2, 1} 9 PARC2e {2, 3} 10 PARC2f {2, 4} 11 PARC2g {3, 1} 12 PARC2h
{3, 2} 13 PARC2i {3, 4} 14 PARC2j {4, 1} 15 PARC2k {4, 2} 16 PARC2l
{4, 3} 17 PARC3a {1, 2, 3} 18 PARC3b {1, 2, 4} 19 PARC3c {1, 3, 4}
20 PARC3d {2, 1, 3} 21 PARC3e {2, 1, 4} 22 PARC3f {2, 3, 4} 23
PARC3g {3, 1, 2} 24 PARC3h {3, 1, 4} 25 PARC3i {3, 2, 4} 26 PARC3j
{4, 1, 2} 27 PARC3k {4, 1, 3} 28 PARC3l {4, 2, 3} 29 PARC4a {1, 2,
3, 4} 30 PARC4b {2, 1, 3, 4} 31 PARC4c {3, 1, 2, 4} 32 PARC4d {4,
1, 2, 3} Note 1: the base station 100 would signal a transmission
format indicator and the mobile terminal 106 would then convert
that into a predefined antenna mapping indicator to determine the
control channel and data channel antenna assignments). Note 2: the
mobile terminal 106 would have a receiving unit 117 that receives
the format indicator from the base station 100 and a processor 119
which accesses and processes instructions that are stored in memory
120 to process the format indicator and to determine which transmit
antenna(s) in the base station 100 are going to be used to #
transmit control data channel information and which are going to be
used to transmit data information.
[0036] In this scheme, the first antenna listed for each format
type specifies the antenna used for the control channel. Thus, this
base station 100 can use 5 bits to specify the combined control
channel antenna assignment and the data antenna assignment since
the control channel antenna is going to be one of the data channel
antennas. In the above table, each entry except for those entries
with one transmit antenna, represents a partial ordering of the
selected transmit antennas. This occurs because the first detected
antenna is designated as the antenna used for the control channel,
however, the remaining antennas can be specified in any order since
the mobile terminal 106 does not rely on such antenna detention
ordering for the detection of the remaining transmitted streams. In
any case, a lower signaling overhead can be achieved by using such
an approach.
[0037] If desired, this table could further be re-arranged in the
manner shown in TABLE 9: TABLE-US-00009 TABLE 9 Transmission Format
Transmission Antenna Indicator Type Mapping 1 PARC1a {1} 2 PARC2a
{1, 2} 3 PARC2b {1, 3} 4 PARC2c {1, 4} 5 PARC3a {1, 2, 3} 6 PARC3b
{1, 2, 4} 7 PARC3c {1, 3, 4} 8 PARC4a {1, 2, 3, 4} 9 PARC1b {2} 10
PARC2d {2, 1} 11 PARC2e {2, 3} 12 PARC2f {2, 4} 13 PARC3d {2, 1, 3}
14 PARC3e {2, 1, 4} 15 PARC3f {2, 3, 4} 16 PARC4b {2, 1, 3, 4} 17
PARC1c {3} 18 PARC2g {3, 1} 19 PARC2h {3, 2} 20 PARC2i {3, 4} 21
PARC3g {3, 1, 2} 22 PARC3h {3, 1, 4} 23 PARC3i {3, 2, 4} 24 PARC4c
{3, 1, 2, 4} 25 PARC1d {4} 26 PARC2j {4, 1} 27 PARC2k {4, 2} 28
PARC2l {4, 3} 29 PARC3j {4, 1, 2} 30 PARC3k {4, 1, 3} 31 PARC3l {4,
2, 3} 32 PARC4d {4, 1, 2, 3}
[0038] In the re-arranged TABLE 9, it can be see that there are 8
entries for each assignment of the control channel information (the
first antenna in the antenna mapping) which could be easily
captured into two of the five designated bits. This format scheme
allows for a partitioning of the signaling bits into two classes of
bits, where two bits are used to specify the control (and data)
channel antenna selection and three bits are used to indicate any
additional data transmission antennas. In particular, two bits are
used to specify the control channel antenna (e.g., assign antenna 1
through antenna 4 to bits {0,0} through bits {1,1}) and these can
be transmitted separately from the remaining bits (e.g., via a
broadcast transmission). The remaining three bits can be assigned
to binary values {0,0,0} to {1,1,1}. For example, in this scheme
for each control antenna assignment, there are 0, 1, 2, or 3
additional antennas which may be assigned for data transmission.
So, if antenna 4 is assigned to the control (and data) channel, and
no additional data antenna is assigned then the base station 100
would use the transmission format indicator 25 in TABLE 9. If
antenna 1 is assigned additionally for data transmission, then the
base station 100 would use the transmission format indicator 26 in
TABLE 9, and so on. If desired, this partitioning may be used to
broadcast the bits corresponding to the control channel antenna
selection, while the additional bits used for the data channel
would be transmitted as part of the downlink signaling to the
corresponding mobile terminal 106. If the antenna selection for the
control channel does not change as rapidly as the antenna selection
for the data transmission, then some amount of signaling overhead
may be saved when the base station 100 and mobile terminals 106
utilize this particular approach.
[0039] From the foregoing, it can be appreciated that the basic
concept of the present solution is to enable the base station 100
to use different aspects of the reported CQI measurements 103 to
select the "best" antenna(s) on which to transmit control channel
information 104 to the mobile terminal(s) 106. For example, in one
aspect a mobile terminal 106 with a receiver 117 may report a CQI
measurement 103 that has a specific antenna detection ordering
associated with it, in which case the base station 100 could place
the control channel on the first detected antenna. A second aspect
may be in a system such as OFDM, where there are multiple CQI
values reported for each antenna over the bandwidth of the OFDM
signal and, consequently, the base station 100 can use sum rates to
help determine which antenna is the best to place the control
channel. Another aspect is the case where there is data to be
transmitted to more then one mobile terminal 106, then the best
antenna 100 can select the "best" antenna(s) in view of the
frequency assignment and antenna selection for each scheduled
mobile terminal 106. Lastly, in another aspect, the base station
100 can use a specific signal format indication to signal the
selected control channel antenna and the data antenna(s) to the
mobile terminal 106.
[0040] Although multiple embodiments of the present invention have
been illustrated in the accompanying Drawings and described in the
foregoing Detailed Description, it should be understood that the
invention is not limited to the disclosed embodiments, but instead
is also capable of numerous rearrangements, modifications and
substitutions without departing from the spirit of the invention as
set forth and defined by the following claims.
* * * * *