U.S. patent application number 13/301519 was filed with the patent office on 2012-07-12 for method for selecting antennas in a wireless networks.
Invention is credited to Noriyuki Fukui, Neelesh B. Mehta, Jia Tang, Koon Hoo Teo.
Application Number | 20120178502 13/301519 |
Document ID | / |
Family ID | 40085588 |
Filed Date | 2012-07-12 |
United States Patent
Application |
20120178502 |
Kind Code |
A1 |
Teo; Koon Hoo ; et
al. |
July 12, 2012 |
Method for Selecting Antennas in a Wireless Networks
Abstract
A method transmits data from a user equipment (UE) including a
transceiver having a set of available antennas. The method selects
a subset of antennas from the set of available antennas; and
transmits the data by the transceiver using the subset of antennas.
The selecting subset of antennas includes transmitting sounding
reference signals (SRSs) according to specified times, frequencies,
and antennas; and receiving, in response to the transmitting the
SRSs, information indicative of a selection of the subset of
antennas.
Inventors: |
Teo; Koon Hoo; (Lexington,
MA) ; Mehta; Neelesh B.; (Bangalore, IN) ;
Tang; Jia; (San Jose, CA) ; Fukui; Noriyuki;
(Yokohama, JP) |
Family ID: |
40085588 |
Appl. No.: |
13/301519 |
Filed: |
November 21, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11834345 |
Aug 6, 2007 |
8086272 |
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13301519 |
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Current U.S.
Class: |
455/562.1 |
Current CPC
Class: |
H04B 7/061 20130101;
H04B 7/0691 20130101 |
Class at
Publication: |
455/562.1 |
International
Class: |
H04W 88/00 20090101
H04W088/00 |
Claims
1. A method for transmitting data from a user equipment (UE)
including a transceiver having a set of available antennas, the
method comprising: selecting a subset of antennas from the set of
available antennas; and transmitting the data by the transceiver
using the subset of antennas, wherein the selecting comprises:
transmitting sounding reference signals (SRSs) according to
specified times, frequencies, and antennas; and receiving, in
response to the transmitting the SRSs, information indicative of a
selection of the subset of antennas.
2. The method of claim 1, wherein the SRS are transmitted in
response to receiving information indicative of the specific times,
frequency and antennas,
3. The method of claim 1, wherein the subset of antennas is
selected by a base station based on the transmitted SRSs, such that
the UE receives the selection from the base station.
4. The method of claim 1, further comprising: transmitting antenna
selection capability information from the transceiver to a base
station; and receiving, in response to transmitting the capability
information, a conformation of the capability information.
5. The method of claim 1, further comprising: performing the
selecting periodically.
6. The method of claim 1, further comprising: performing the
selecting adaptively.
7. The method of claim 1, further comprising: performing the
selecting based on hopping SRSs.
8. The method of claim 1, further comprising: performing the
selecting based on wideband SRSs.
9. The method of claim 1, further comprising: performing the
selecting based on variable bandwidth SRSs.
10. The method of claim 1, further comprising: performing the
selecting based on narrow-band SRSs.
11. The method of claim 1, further comprising: receiving antenna
selection parameters including one or combination of transmission
bandwidth, starting or ending bandwidth position, transmission
period, cyclic shift hopping sequence, transmission sub-frame,
repetition factor for indicating a density of a pilot subcarriers,
a duration of the SRS transmission, symbol position of the SRS
within a sub-frame, and hopping SRS related parameters.
12. A user equipment (UE) forming at least part of a wireless
network, comprising: a set of available antennas; at least one RF
chain, wherein a number of available antennas of the UE is greater
than a number of RF chains; and a means for transmitting the SRSs
according to specified times, frequencies, and antennas, and for
receiving, in response to the transmitting the SRSs, information
indicative of a selection of the subset of antennas, wherein the RF
chain transmits data using the selected subset of antennas.
13. The UE of claim 12, wherein the SRS are transmitted in response
to receiving information indicative of the specific times,
frequency and antennas,
14. The UE of claim 12, wherein the subset of antennas is selected
by a base station based on the transmitted SRSs, such that the UE
receives the selection from the base station.
15. The UE of claim 12, wherein the means for transmitting the SRS
and for receiving the information is a transceiver including a
processor.
16. A method for transmitting data from a transceiver having a set
of available antennas and at least one RF chain, wherein a number
of available antennas in the set is greater than a number of RF
chains, wherein the transceiver is a part of a wireless network
including a base station and a plurality of transceivers, the
method comprising: transmitting, to the base station, sounding
reference signals (SRSs) according to specified times, frequencies,
and antennas; receiving, from the base station in response to the
transmitting the SRSs, information indicative of a selection of the
subset of antennas; and transmitting the data to the base station
using the subset of antennas.
17. The method of claim 16, wherein the SRSs are transmitted in
response to receiving from the base station information indicative
of specific times, frequency and antennas.
Description
PRIORITY APPLICATION
[0001] This application is a Continuation of prior U.S. patent
application Ser. No. 11/834,345, filed Aug. 6, 2007, by Mehta et
al.
FIELD OF INVENTION
[0002] This invention relates generally to antenna selection in
wireless networks, and more particularly to selecting antennas in
wireless networks.
BACKGROUND OF THE INVENTION
[0003] OFDM
[0004] Orthogonal frequency division multiplexing (OFDM) is a
multi-carrier communication technique, which employs multiple
orthogonal sub-carriers to transmit parallel data streams. Due to
the relatively low symbol-rate on each of the sub-carriers, OFDM is
robust to severe channel conditions, such as frequency attenuation,
narrowband interference, and frequency-selective fading. By
prepending a cyclic prefix (CP) in front of each symbol, OFDM can
eliminate inter-symbol interference (ISI) when the delay spread of
the channel is shorter than the duration of CP. OFDM can also
simplify frequency-domain channel equalization because the multiple
sub-carriers are orthogonal to each other to eliminate
inter-carrier interference (ICI).
[0005] OFDMA
[0006] When OFDM is combined with a multiple access mechanism, the
result is orthogonal frequency division multiplexed access (OFDMA).
OFDMA allocates different sub-carriers or groups of sub-carriers to
different transceivers (user equipment (UE)). OFDMA exploits both
frequency and multi-user diversity gains. OFDMA is included in
various wireless communication standards, such as IEEE 802.16 also
known as Wireless MAN. Worldwide Interoperability for Microwave
Access (WiMAX) based on 802.16 and the 3.sup.rd generation
partnership project (3GPP) long-term evolution (LTE), which has
evolved from Global System for Mobile Communications (GSM), also
use OFDMA.
[0007] SC-FDMA Structure in LTE Uplink
[0008] The basic uplink (UL) transmission scheme in 3GPP LTE is
described in 3GPP TR 25.814, v7.1.0, "Physical Layer Aspects for
Evolved UTRA," incorporated herein by reference. That structure
uses a single-carrier FDMA (SC-FDMA) with cyclic prefix (CP) to
achieve uplink inter-user orthogonality and to enable efficient
frequency-domain equalization at the receiver side. This allows for
a relatively high degree of commonality with the downlink OFDM
scheme such that the same parameters, e.g., clock frequency, can be
used.
[0009] Antenna Selection
[0010] The performance of the system can be enhanced by
multiple-input-multiple-output (MIMO) antenna technology. MIMO
increases system capacity without increasing system bandwidth. MIMO
can be used to improve the transmission reliability and to increase
the throughput by appropriately utilizing the multiple spatially
diverse channels.
[0011] While MIMO systems perform well, they may increase the
hardware cost, signal processing complexity, power consumption, and
component size at the transceivers, which limits the universal
application of MIMO technique. In particular, the RF chains of MIMO
systems are usually expensive. In addition, the signal processing
complexity of some MIMO methods also increases exponentially with
the number of antennas.
[0012] While the RF chains are complex and expensive, antennas are
relatively simple and cheap. Antenna selection (AS) reduces some of
the complexity drawbacks associated with MIMO systems. In an
antenna selection system, a subset of an set of the available
antennas is adaptively selected by a switch, and only signals for
the selected subset of antennas are processed by the available RF
chains, R1-063089, "Low cost training for transmit antenna
selection on the uplink," Mitsubishi Electric, NTT DoCoMo, 3GPP
RAN1#47, R1-063090, "Performance comparison of training schemes for
uplink transmit antenna selection," Mitsubishi Electric, NTT
DoCoMo, 3GPP RAN1#47, R1-063091, "Effects of the switching duration
on the performance of the within TTI switching scheme for transmit
antenna selection in the uplink," Mitsubishi Electric, NTT DoCoMo,
3GPP RAN1#47, and R1-051398, "Transmit Antenna Selection Techniques
for Uplink E-UTRA," Institute for Infocomm Research (I2R),
Mitsubishi Electric, NTT DoCoMo, 3GPP RAN1#43, R1-070524,
"Comparison of closed-loop antenna selection with open-loop
transmit diversity (antenna switching between TTIs)," Mitsubishi
Electric, 3GPP RAN1#47bis, R1-073067, "Adaptive antenna switching
with low sounding reference signal overhead," Mitsubishi Electric,
3GPP RAN1#49bis, R1-073068, "Impact of sounding reference signal
loading on system-level performance of adaptive antenna switching,"
Mitsubishi Electric, 3GPP RAN1#49bis, all incorporated herein by
reference.
[0013] Signaling and Protocol Design for Antenna Selection
[0014] A signaling format for indicating a selected antenna is
described in R1-070860, "Closed loop antenna switching in E-UTRA
uplink," NTT DoCoMo, Institute for Infocomm Research, Mitsubishi
Electric, NEC, Sharp, Toshiba Corporation, 3GPP RAN1#48,
incorporated herein by reference. In order to indicate one antenna
out of two possible antennas (A and B), that scheme uses 1 of bit
information, either explicitly or implicitly, into an "uplink
scheduling grant" message, which indicates the antenna selection
decision, 0 means antenna A, and 1 indicates antenna B.
[0015] In the prior art, antenna selection is typically performed
using pilot signals. Furthermore, antenna selection has been
performed only for small-range indoor wireless LANs (802.11n), and
where only a single user is on a wideband channel at any one time,
which greatly simplifies antenna selection.
[0016] In the prior art, sounding reference signals (SRS) and data
demodulation (DM) reference signals are only used for frequency
dependent scheduling.
[0017] A protocol and exact message structure for performing
antenna selection for large-range, outdoor OFDMA 3GPP networks is
not known at this time. It is desired to provide this protocol and
message structure for performing antennas selection for an uplink
of an OFDMA 3GPP wireless network.
SUMMARY OF THE INVENTION
[0018] One embodiment of invention discloses a method for
transmitting data from a user equipment (UE) including a
transceiver having a set of available antennas. The method selects
a subset of antennas from the set of available antennas; and
transmits the data by the transceiver using the subset of antennas.
The selecting subset of antennas includes transmitting sounding
reference signals (SRSs) according to specified times, frequencies,
and antennas; and receiving, in response to the transmitting the
SRSs, information indicative of a selection of the subset of
antennas.
[0019] Usually, the SRS are transmitted in response to receiving
information indicative of the specific times, frequency and
antennas. Also, the subset of antennas can be selected by a base
station based on the transmitted SRSs, such that the UE receives
the selection from the base station.
[0020] Another embodiment discloses a user equipment (UE) forming
at least part of a wireless network. The UE includes a set of
available antennas; at least one RF chain, wherein a number of
available antennas of the UE is greater than a number of RF chains;
and a means for transmitting the SRSs according to specified times,
frequencies, and antennas, and for receiving, in response to the
transmitting the SRSs, information indicative of a selection of the
subset of antennas, wherein the RF chain transmits data using the
selected subset of antennas. In one variation of this embodiment,
the means for transmitting the SRS and for receiving the
information is a transceiver including a processor.
[0021] Yet another embodiment discloses a method for transmitting
data from a transceiver having a set of available antennas and at
least one RF chain, wherein a number of available antennas in the
set is greater than a number of RF chains, wherein the transceiver
is a part of a wireless network including a base station and a
plurality of transceivers. The method includes steps of
transmitting, to the base station, sounding reference signals
(SRSs) according to specified times, frequencies, and antennas;
receiving, from the base station in response to the transmitting
the SRSs, information indicative of a selection of the subset of
antennas; and transmitting the data to the base station using the
subset of antennas.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1A is a block diagram of a wireless network according
to an embodiment of the invention;
[0023] FIG. 1B is a block diagram of a frame according to an
embodiment of the invention;
[0024] FIG. 1C is a method for selecting antennas according to an
embodiment of the invention;
[0025] FIG. 2A is a block diagram of sub-frame structure according
to an embodiment of the invention;
[0026] FIG. 2B is a block diagram of time-slot structure according
to an embodiment of the invention;
[0027] FIG. 2C is a block diagram of a resource block according to
an embodiment of the invention;
[0028] FIG. 3 is a block diagram of the Level-A registration
signaling procedure according to an embodiment of the
invention;
[0029] FIG. 4 is a block diagram of legend descriptions used for
FIGS. 5A to 8B according to embodiments of the invention;
[0030] FIGS. 5A to 8B are block diagrams of protocols for Option1
signaling according to embodiments of the invention;
[0031] FIG. 9 is a block diagram of legend description used for
FIGS. 10A to 13B according to embodiments of the invention; and
[0032] FIGS. 10A to 13B are block diagrams of protocols for Option2
signaling according to embodiments of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0033] LTE System Overview
[0034] FIG. 1 shows the general structure of an OFDMA 3GPP LTE
wireless network according to an embodiment of the invention.
Multiple user equipments (UEs) or transceivers 111-113 communicate
with a base station 110. It should be understood that the base
station also operates as a transceiver. However, hereinafter,
reference to transceivers means UE, unless specified otherwise. It
should be noted that invention can also be used with SC-FDMA and
OFDM networks.
[0035] The base station is called an evolved Node B (eNodeB) in the
3GPP LTE standard. The eNodeB 110 manages and coordinates all
communications with the transceivers in a cell using connections
101, 102, 103. Each connection can operate as a downlink from the
base station to the UE or an uplink from the UE to the base
station. Because the transmission power available at the base
station is orders of magnitude greater than the transmission power
at the UE, the performance on the uplink is much more critical.
[0036] To perform wireless communication, both the eNodeB and the
transceivers are equipped with at least one RF chain and one
antenna. Normally, the number of antennas and the number RF chains
are equal at the eNodeB. The number of antennas at the base station
can be quite large, e.g., dozens. However, due to the limitation on
cost, size, and power consumption, UE transceivers usually have
less RF chains than antennas 115. The number of antennas available
at the UE is relatively small, e.g., two or four, when compared
with the base station. Therefore, antenna selection as described is
applied at the transceivers. However, the base station can also
perform the antenna selection as described herein.
[0037] Generally, antennas selection selects a subset of antennas
from a set of available antennas at the transceivers.
[0038] LTE Frame Structure
[0039] FIG. 1B shows the basic structure of a 10 ms frame 200
according to an embodiment of the invention. The horizontal axis
indicates time and the vertical axis indicates frequency. The frame
includes ten 1 ms sub-frames 210 in the time domain. The frame is
also partitioned into frequency bands 220, e.g. fifty. The number
of bands depends on the total bandwidth of the channels, which can
be in the ranges of several megaHertz. Each sub-frame/band
constitutes a resource block, see inset 230 and FIG. 2C for
details.
[0040] Method
[0041] FIG. 1C shows the basic method for antenna selection
according to an embodiment of the invention. The base station 110
specifies times and frequencies to transmit sounding reference
signals (SRSs) 161, and specifies which antennas of the set of
available antennas to use to transmit the SRSs for the specified
times and frequencies. The transceiver 101 transmits the SRSs 161
according to the specified times, frequencies, and antennas
151.
[0042] The base station selects 170 a subset of antennas 181 based
on the received SRSs 161. The base station then indicates 180 the
selected subset of antenna 181 to the transceiver. Subsequently,
the transceiver 101 can transmit 190 data 191 using the selected
subset of antennas 181. The transceiver can also use the same
subset of antennas for receiving data from the base station.
[0043] LTE Frame Structure
[0044] FIG. 2A shows a general structure of a sub-frame according
to an embodiment of the invention. In 3GPP LTE, the transmission
time of a frame is partitioned into TTIs (transmission time
interval) 201 of duration 1.0 ms. The terms `TTI` and `sub-frame`
are used interchangeably. The frame is 10 ms long, which includes
10 TTIs. The TTIs include time-slots 202.
[0045] FIG. 2B shows a general structure of a time-slot according
to an embodiment of the invention. As described above, the TTI is
the basic transmission unit. One includes two equal length
time-slots 202 each with a duration of 0.5 ms. The time-slot
includes seven long blocks (LB) 203 for symbols. The LBs are
separated by cyclic prefixes (CP) 204. In total, one TTI comprises
fourteen LB symbols. It should be noted that the invention is not
limited to a specific frame, sub-frame, or time-slot structure.
[0046] FIG. 2C shows the details of one resource block (RB) 230
during one TTI 201 according to an embodiment of the invention. The
TTI is partitioned, in time, into fourteen LBs 203. Each LB can
carry a symbol. The entire system bandwidth, e.g., of 5 MHz or 10
MHz or 20 MHz, is partitioned divided into sub-carriers 205 at
different frequencies. Groups of twelve contiguous sub-carriers, as
shown, within one TTI are called resource blocks (RBs). For
example, 10 MHz of bandwidth within 1 TTI might include fifty RBs
in the frequency domain. The two shaded LBs 210, i.e., the 4.sup.th
and 11.sup.th LBs, carry data demodulation (DM) reference signals
(RS) that are known to the receiver. The DM RS enables the receiver
to estimate the channel state of the RBs assigned to the
transceiver and coherently demodulate the unknown data carried in
the other LBs. That is, in the prior art, DM reference signals are
only used for channel estimation prior to data demodulation. For
clarity the CPs are not shown in FIG. 2C. It should be noted that
the invention is not limited to a specific number of LBs during the
TTI or the location of the DM RSs in the TTI. According to one
embodiment of the invention, the DM reference signal is also used
for antenna selection.
[0047] Sounding Reference Signal (SRS)
[0048] Except for the 4.sup.th and the 11.sup.th LBs, the other LBs
are used for transmitting control and data signals, as well as
uplink sounding reference signals (SRS). For instance, the first LB
can carry the SRS. The SRS is usually a wideband or variable
bandwidth signal. The SRS enables the base station to estimate the
frequency response of the entire system bandwidth or a portion
thereof. This information enables the base station to perform
resource allocation such as uplink frequency-domain scheduling.
[0049] According to the embodiment of the invention, the SRSs are
also used for antenna selection.
[0050] Another option considered for 3GPP LTE is a
frequency-hopping (FH) based SRS. Specifically, a hopping SRS, with
a bandwidth smaller than the system bandwidth, is transmitted based
on a pre-determined hopping pattern. The hopped SRSs, over multiple
transmissions, span a large portion of the system bandwidth or even
the entire system bandwidth. With frequency hopping the probability
that transceivers interfere with each other during sounding is
decreased.
[0051] In 3GPP LTE, the eNodeB can enable and disable SRS
transmission by the UE transceiver. Moreover, when antenna
selection is enabled, the eNodeB can specify the SRS parameters to
the transceiver, including transmission bandwidth, starting or
ending bandwidth position, transmission period, cyclic shift
hopping sequence, transmission sub-frame, repetition factor for
indicating the density of the pilot subcarriers in the SRS LB,
duration of SRS transmission, symbol position of SRS within a
sub-frame, and hopping SRS related parameters, among others.
Furthermore, to support antenna selection by using SRS, the same
SRS is used by all antennas. Thus, the eNodeB knows in advance,
which antenna is sending the SRS.
[0052] In one embodiment of the invention, we describe a format and
protocol for antenna selection by using SRS in the 3GPP LTE
wireless network. When SRS are used for antenna selection, the SRS
is called an antenna selection SRS (A-SRS). Otherwise, the SRS is
called a regular SRS (R-SRS). Making the A-SRS protocol compatible
with the R-SRS protocol ensures that extra signaling overhead
associated with A-SRS is as low as possible.
[0053] Signaling for Antenna Selection
[0054] In general, our invention comprises three levels of
messages, namely, Level-A registration signaling, Level-B slow
signaling, and Level-C fast signaling, all or some of which can be
used for antenna selection. A summary of the possible signaling
messages for enabling antenna selection is shown in Table 1A and
Table 1B, where the two tables correspond to two slightly different
signaling options: Option1 and Option2.
[0055] The major difference between Option1 and Option2 is the "SRS
start/stop" message. The "SRS start/stop" is a Level-B message in
Option1 and a Level-C message in Option2. In the following, we
first describe Option1 in details. Then, we describe Option2 by
mainly focusing on the differences between the two options.
TABLE-US-00001 TABLE 1A Signaling messages for antenna selection
[Option1] Message Size Field Layer (bits) Comment UL Level-A: L3
[1] The UE notifies eNodeB if UE Registration supports uplink
antenna selection. DL Level-A: L3 [1] The eNodeB notifies UE if
eNodeB Registration supports antenna selection. Level-B: L3 [FFS]
SRS start/stop. Slower b) Enable/disable A-SRS, and set up
Signaling A-SRS parameters when AS is enabled. Level-C: L1 [1]
Antenna selection decision about Faster which subset of antennas UE
should Signaling use for transmission. In the above table, "FFS"
means "for further specification.
TABLE-US-00002 TABLE 1B Signaling messages for antenna selection
[Option2] Message Size Field Layer (bits) Comment UL Level-A: L3
[1] The UE notifies eNodeB if UE Registration supports uplink
antenna selection. DL Level-A: L3 [1] The eNodeB notifies UE if
eNodeB Registration supports antenna selection. Level-B: L3 [FFS]
Enable/disable A-SRS, and set up Slower A-SRS parameters when AS is
Signaling enabled. Level-C: L1 [3] SRS start/stop. Faster b)
Antenna selection decision about Signaling which subset of antennas
UE to use for transmission (and reception).
[0056] Signaling Description for [Option1]
[0057] As shown in Table 1A, the Level-A registration signaling
indicates whether both the transceiver and the eNodeB support
uplink (UL) antenna selection. If the eNodeB does not support
antenna selection but the transceiver does, the transceiver can use
open-loop antenna selection, which does not require any support
from the eNodeB. This information is exchanged between the
transceiver and the eNodeB at the beginning of the communications,
for example, when the transceiver registers with the wireless
network upon entry.
[0058] Level-B is a layer 3 (or radio resource control (RRC) layer)
signaling that is used to set up AS training parameters for the
SRS. Level-B is a slow form of signaling that is used infrequently.
The eNodeB uses Level-B signaling to stop and start the transceiver
to send the A-SRS, or to change the A-SRS parameters.
[0059] Level-C is fast signaling that is used by the eNodeB to
communicate to the transceiver its antenna selection decisions, and
to enable the antenna selection to track short-term variations due
to channel fading.
[0060] In the uplink (UL), only the Level-A message is needed from
the transceiver to notify the eNodeB of its capability of
supporting AS. In the downlink (DL), some or all of the three
levels of messages may be necessary.
[0061] Level-A Signaling
[0062] The Level-A registration signaling is used to indicate if
both the transceiver and the eNodeB support uplink antenna
selection. This information is exchanged between the transceiver
and the eNodeB when the transceiver enters the network and before
beginning data communications.
[0063] The basic procedure between transceiver and eNodeB to
exchange the registration information is shown in FIG. 3. In the
uplink (UL), 1-bit information is required for the UE transceiver
301 to notify the base station eNodeB 302 whether it is an antenna
selection capable transceiver, or not. Similarly, in the downlink
(DL), 1-bit information is needed for the eNodeB 302 to inform the
transceiver about its capability to support uplink transmit AS.
[0064] In one embodiment of the invention, we include the 1-bit
uplink Level-A signaling in the "UE capability information" message
303 sent by the transceiver, and include the 1-bit downlink Level-A
signaling into "UE capability information confirm" message 304 sent
by the eNodeB.
[0065] The "UE capability information" contains a "radio access
capability" field. The "radio access capability" field further
comprises a "physical channel capability" field. Similar to the "UE
MIMO support" already included in the "physical channel
capability", a 1-bit "UE AS support" field is added into the
"physical channel capability" to indicate the UE's antenna
selection capability.
[0066] It is also possible to include the above Level-A signaling
information into other messages. Depending on how the radio
resource control (RRC) protocol is designed in 3GPP LTE, the
Level-A signaling can be adjusted accordingly.
[0067] Level-B Signaling
[0068] The frame structure for Level-B message [Option1] is shown
in Table 2. The Level-B signaling is used to set up AS parameters.
This information is required when the eNodeB requests the
transceiver to start or stop sending the SRS, or to change A-SRS
parameters. R-SRS and A-SRS share the same Level-B signaling
message, except that two fields (i.e., "A-SRS Enable" and "Period2"
shown in boldface in Table 2) are for A-SRS. It should be noted
that all the message format descriptions provided herein are only
examples and variations are possible within the scope of this
invention.
TABLE-US-00003 TABLE 2 Frame structure for Level-B message
[Option1] Size Field (bits) Comment SRS Start/Stop [1] Request to
start (when set to 1) or stop (when set to 0) sending SRS. A-SRS
Enable [1] A-SRS is enabled (when set to 1) or R-SRS is enabled
(when set to 0). Periodic/Adaptive [1] Indicates whether the SRS is
performed periodically (when set to 1, until told to stop) or
adaptively (when set to 0, one- shot SRS). BW & Position [FFS]
The bandwidth (in terms of number of RBs) and the starting position
(in terms of RB index) for the SRS. Start Sub-frame [FFS] The index
of the subframe within a radio frame that the UE starts sending the
SRS. Symbol Position [FFS] The index of the LB within a sub-frame
at which the SRS is located (SRS is not necessary at the 1.sup.st
LB of a sub-frame). Period1 [FFS] The interval (in terms of number
of TTIs) between two consecutive SRSs. This value does not matter
for non- hopping adaptive R-SRS. Period2 [FFS] The interval (in
terms of number of SRSs) between two consecutive A-SRSs and pattern
of transmission. Hopping Related [FFS] Indicates hopping related
information Fields such as number of hops, hopping pattern,
etc.
[0069] The field "SRS Start/Stop", when set to 1, indicates the
request from the eNodeB to start sending SRS (for both A-SRS and
R-SRS cases). Otherwise, when this bit is set to 0, then the eNodeB
requests the transceiver to stop sending SRS.
[0070] The field "A-SRS Enable", when set to 1, indicates that the
A-SRS is enabled. Then, all the other fields of this message are
used for setting up A-SRS parameters. The meaning of each field is
described in the "Comment" column of Table 2. If "A-SRS Enable" is
set to 0, then R-SRS is enabled. Thus, the other fields (except
"Period2") of this message are used for setting up R-SRS
parameters. By sharing parameter fields with R-SRS, the overhead
for enabling A-SRS is low.
[0071] The field "Period1" indicates the interval (in terms of
number of TTIs) between any two consecutive SRSs, which is used for
both A-SRS and R-SRS. The field "Period2", on the other hand, is
only used for periodic A-SRS, which indicates the interval between
two consecutive A-SRSs as well as the pattern of transmission of
the A-SRS. By using "Period2", the eNodeB can dynamically adjust
the portion of the SRSs that are sent from the unselected antenna,
achieving a tradeoff between the performance and the
antenna-switching overhead. The value "Period2" should be no less
than 2. If Period2=2, then the SRS is alternatively transmitted
from the selected antenna and the unselected antenna.
[0072] Upon receiving the Level-B message, the transceiver first
checks the "SRS Start/Stop" field. If "SRS Start/Stop=0", then the
transceiver stops sending SRS. The other fields of this message are
omitted. Otherwise, if "SRS Start/Stop=1", then the transceiver is
told to start sending SRS according to the format (e.g., either
A-SRS or R-SRS; either periodic or adaptive, etc) defined in the
parameter list.
[0073] A number of variations for the structure of the above
Level-B message are possible. First, all the fields need not be
sent together at the same time. Depending on the function
categories, the Level-B message might be split into sub-messages
and sent separately. Second, the 1-bit field "A-SRS Enable" can be
inside another field of this message. Depending on how R-SRS
signaling is designed in 3GPP LTE, A-SRS signaling may need to be
adjusted accordingly in compliance with R-SRS.
[0074] Level-C Signaling
[0075] The frame structure for Level-C message [Option1] is shown
in Table 3. The Level-C fast signaling message is used to signal
the transceiver about which antenna to use for data transmission.
For selecting one antenna out of two possible candidates, a 1-bit
information field suffices. One option is to include this 1-bit
information in the "uplink scheduling grant" message. It should be
noted that all the message format descriptions provided herein are
only examples.
TABLE-US-00004 TABLE 3 Frame structure for Level-C message
[Option1] Size Field (bits) Comment Resource ID (UE or [8-9]
Indicates the UE (or group of UEs) assignment group specific) for
which the grant is intended Resource FFS Indicates which uplink
resources, assignment localized or distributed, the UE is allowed
to use for uplink data transmission. AS [1] Indicates the decision
on which Decision subset of the antennas is selected for data
transmission Duration of [2-3] The duration for which the assign-
assignment ment is valid. The use for other purposes is FFS. TF
Transmission FFS The uplink transmission parameters parameters
(modulation scheme, payload size, MIMO-related information, etc)
the UE shall use.
[0076] The "uplink scheduling grant" is used by the eNodeB to make
an uplink scheduling decision for a transceiver specified by the
"ID" field. In the "resource assignment" field, the eNodeB notifies
the transceiver which RBs are assigned for its data transmission.
The 1-bit antenna selection decision can be created in this field.
Thus, when antenna selection is enabled, the "resource assignment"
field indicates a joint scheduling and antenna selection
decision.
[0077] The "AS Decision" bit, when set to 1, indicates that the
transceiver should switch to a different transmit antenna to
transmit data. If this field is set to 0, then the transceiver uses
the same antenna to transmit data. Upon receiving this message, the
transceiver continues to use the same antenna, or switches to a
different antenna, according to the decision made by the eNodeB.
The above method corresponds to a "relative antenna index" based
approach. That is, the eNodeB does not know exactly which antenna
is used. Instead, the eNodeB just notifies the transceiver to
either "switch" or "not switch" the subset of selected antennas. It
is also possible to use an "absolute antenna index" based approach
to indicate the antenna selection decision, where the eNodeB
notifies the transceiver either to use the antenna or the 2.sup.nd
antenna, or otherwise designated subsets.
[0078] It should be noted that it is also possible to include the
AS decision information in other fields (e.g., "TF" field) of the
uplink scheduling grant message, or even inside other message.
[0079] Signaling Description for [Option2]
[0080] As shown in Table 1B, [Option2] is similar to [Option1]
except for the "SRS start/stop" message, which is a Level-B message
in [Option1] and a Level-C message in [Option2]. The advantage of
[Option2] is that the SRSs (both R-SRS and A-SRS) can be configured
quickly to start/stop (especially stop) for granting a priority to
other transceivers. However, the disadvantage is the slightly
larger payload of the Level C messages.
[0081] In [Option1], the A-SRS parameters are combined together
with SRS request (either to start or stop). In [Option2], the A-SRS
parameters and SRS request are sent separately. Therefore, in
[Option2], the Level-B message does not include "SRS start/stop"
field (i.e., the first field in Table 2). Meanwhile, 2 bits are
added to the Level-C message in order to achieve the same "SRS
start/stop" function. Thus, a total of 3 bits are required for
Level-C message in [Option2].
[0082] The fields that constitute a Level-C message [Option2] are
shown in Table 4. The Level-C message is used to indicate A-SRS
request start or stop and antenna selection decision. In one
embodiment of the invention, we include this 3-bit information in
"uplink scheduling grant" message. It should be noted that all the
message format descriptions provided herein are only examples.
TABLE-US-00005 TABLE 4 Frame structure for Level-C message
[Option2] Size Field (bits) Comment Resource ID (UE or [8-9]
Indicates the UE (or group of UEs) assignment group for which the
grant is intended specific) Resource FFS Indicates which uplink
resources, assignment localized or distributed, the UE is allowed
to use for uplink data transmission. SRS Start [1] Request to start
(when set to 1) sending SRS. Otherwise (when set to 0), keep
current status. SRS Stop [1] Request to stop (when set to 1)
sending SRS. Otherwise (when set to 0), keep current status. AS [1]
Indicates which transmit antenna is Decision selected for UL data
transmission Duration [2-3] The duration for which the assignment
of is valid. The use for other purposes, assignment e.g., to
control persistent scheduling, `per process` operation, or TTI
length, is FFS. TF Transmission FFS The uplink transmission
parameters parameters (modulation scheme, payload size,
MIMO-related information, etc) the UE shall use. If the UE is
allowed to select (part of) the transport format, this field sets
determines an upper limit of the transport format the UE may
select.
[0083] Upon receiving the Level-C message, the transceiver checks
"SRS start" and "SRS stop" bits. If either bit is set to 1, then
this message contains the eNodeB's request to either start or stop
sending SRS. When "SRS start=1", the transceiver is told to start
sending SRS based on the Level-B parameters. It is assumed that the
transceiver has already obtained the Level-B parameters in advance
in a separate message (or transceiver can store a set of default
Level-B parameters). When "SRS stop=1", then the transceiver stops
sending the SRS. However, it is possible that both bits are 0. In
this case, the transceiver keeps its current SRS status, until
either "SRS start" or "SRS stop" is set to 1.
[0084] The transceiver also checks the "AS Decision" bit. The
responses to "AS Decision" bit are the same as [Option1] at
transceiver.
[0085] It should be noted that it is also possible to include "SRS
Start" and "SRS Stop" information inside another field (e.g., "TF"
field) of the uplink scheduling grant message, or even inside other
message. Also, the "SRS Start" and "SRS Stop" can be at a separate
message from the "AS Decision". In this case, the "SRS Start" and
"SRS Stop" can be combined together into 1 bit, just as that in
[Option1]. However, A-SRS and R-SRS share the same SRS request.
Depending on how R-SRS signaling will be designed in 3GPP LTE,
A-SRS signaling may need to be adjusted accordingly in compliance
with R-SRS.
[0086] Protocol for Antenna Selection
[0087] In one embodiment of the invention, our protocol utilizes
the sounding reference signal (SRS) 161 for uplink transmit antenna
selection, R1-073067, "Adaptive antenna switching with low sounding
reference signal overhead," Mitsubishi Electric, 3GPP RAN1#49bis,
R1-073068, "Impact of sounding reference signal loading on
system-level performance of adaptive antenna switching," Mitsubishi
Electric, 3GPP RAN1#49bis. The antenna switching is performed
within a TTI, but we do not preclude between TTI switching,
R1-063089, "Low cost training for transmit antenna selection on the
uplink," Mitsubishi Electric, NTT DoCoMo, 3GPP RAN1#47, R1-063090,
"Performance comparison of training schemes for uplink transmit
antenna selection," Mitsubishi Electric, NTT DoCoMo, 3GPP RAN1#47,
and U.S. patent application Ser. No. 11/620,105, "Method and System
for Antenna Selection in Wireless Networks" filed by Mehta et al.
on Jan. 5, 2007, incorporated herein by reference.
[0088] In terms of functionality, the protocol is flexible and
applicable to different antenna selection scenarios. First, both
periodic antenna selection and adaptive antenna selection are
supported. In particular, the protocol can switch between different
periodic AS (with different sounding intervals), or between
different adaptive AS (with different sounding intervals), or
between periodic and adaptive AS, or even allow them together, as
dictated by the eNodeB. Second, both non-hopping SRS based and
hopping SRS based antenna selections are supported. The protocol
can also switch between them as dictated by eNodeB. Third, the
protocol supports antenna selection based on different SRSs,
including wideband SRS, variable bandwidth SRS, and narrow-band
SRS. Fourth, the protocol supports antenna selection for packet
retransmission in both asynchronous HARQ and synchronous HARQ
modes.
[0089] The current protocol focuses on 1 out of 2 antenna
selection, while the extension to multiple antenna selection is
possible with a cost of additional signaling overhead.
[0090] Protocol Description for [Option1]
[0091] FIG. 4 shows the legend for protocol [Option1], which is
used for the FIG. 5A to FIG. 8B, according to an embodiment of the
invention. The legends are intended to simplify the details of the
otherwise complex drawings. The legends are Wideband or variable
bandwidth SRS 401, Narrow-band hopping SRS 402, Data block
(sub-frame) if no SRS is sent at the same TTI 403, Data block
(sub-frame) if SRS is sent at the same TTI 404, No data to send in
a TTI 405, Level-B slower signaling: SRS parameters & SRS
request 406, and Level-C faster signaling: AS & scheduling
decision 407.
[0092] For clarity Level-A signaling exchange is omitted herein. It
should be noted that all the protocols herein are only
examples.
[0093] No Frequency Hopping--Wideband SRS and Variable BW SRS
[0094] Periodic SRS: FIGS. 5A and 5B show the protocol illustration
for non-hopping periodic A-SRS and R-SRS, respectively. As shown in
FIG. 5A, at the 1.sup.st TTI of a frame, the eNodeB sends a set of
SRS parameters 501, which includes an "SRS Start" request. The
detailed parameters are listed at the bottom-left corner 502 in
FIG. 5A. The transceiver receives this request at the 2.sup.nd TTI
503, and gets ready to send SRS as per the parameters. Based on the
parameter 502, at the 3.sup.rd TTI (i.e., Start_Subframe=3), the
transceiver starts sending SRS 504, and will periodically send the
SRS from the two antennas at every TTI (i.e., Period1=1, until told
to stop). Based on received SRS 504, the eNodeB can make a joint
scheduling and AS decision 505. The transceiver receives the
decision in the 5.sup.th TTI 506, and will react with a certain TTI
delay. The decision can be either a resource block assignment or an
antenna selection decision or both. Note that in some TTI 507,
there is no data to send, but the transceiver still needs to send
SRS periodically as required. Also note that the eNodeB can make
decision 508 at any time, not necessary periodically.
[0095] Because "Period2=3", one out of every 3 SRSs is sent from
the unselected antenna. As shown in FIG. 5A, the SRS 509 at the
5.sup.th TTI, the SRS 510 at the 8.sup.th TTI, and the SRS 511 at
the 1.sup.st TTI of the next frame, are sent from the unselected
antenna, while the rest SRSs are sent from the selected
antenna.
[0096] For comparison purpose, FIG. 5B shows the protocol for
non-hopping periodic R-SRS, which can be seen from the parameter
512 with "AS Enable=0". The difference is that the decision from
eNodeB is only a scheduling decision, not an antenna switching
decision. The SRSs are sent periodically every 2 TTIs
("Period1=2"). The "Period2" field is no use for R-SRS case.
[0097] In FIGS. 5A and 5B, the parameter "Num_Hops=1" means that
the entire bandwidth is covered by 1 hop. That is, no frequency
hopping is involved. If "Num_Hops>1", then frequency hopping is
applied for SRS.
[0098] It should be noted that in the example protocols, we assume
a certain delay for the eNodeB to make AS and scheduling decision,
and a certain delay for the transceiver to react to the eNodeB's
instruction. The delay depends on the standard specification, and
the values provided herein are only examples.
[0099] Adaptive SRS: FIGS. 6A and 6B show the protocol for
non-hopping adaptive A-SRS and R-SRS, respectively. Compared to the
case with periodic antenna selection where the SRSs are sent
periodically (until told to stop), adaptive SRS is a "one-shot" SRS
transmission as per the eNodeB's request. For the A-SRS shown in
FIG. 6A, two SRSs are sent by the two antennas successively, with
the interval determined by the "Period1" field in the parameter
list. Similar to the periodic case, the eNodeB makes scheduling
and/or AS decision based on the received A-SRSs. For the R-SRS
shown in FIG. 6B, only one SRS is sent by the transmit antenna.
Therefore, the "Period1" field is of no use in this case.
[0100] Frequency Hopping--Narrow-band SRS
[0101] Periodic SRS: FIGS. 7A and 7B show the protocol for hopping
periodic A-SRS and R-SRS, respectively. For example purposes, we
assume that the entire bandwidth is covered by 2 hops (Num_Hops=2),
and each narrow-band SRS spans half of the available bandwidth. As
shown in FIG. 7A, in order to make each of the two antennas sound
the entire bandwidth, a total of 4 SRSs are required in each
sounding cycle. The interval between two consecutive SRSs is
determined by "Period1" field of the parameter list 701 (it is set
to 1 in the figure as an example). Similar to the non-hopping case,
because "Period2=3" in the parameter list 701, one out of every 3
SRSs is sent from the unselected antenna. Specifically, the SRS 702
at the 5.sup.th TTI, the SRS 703 at the 8.sup.th TTI, and the SRS
704 at the 1.sup.st TTI of the next frame, are sent from the
unselected antenna, while the rest SRSs are sent from the selected
antenna. The eNodeB can make a scheduling and AS decision each time
when it receives an A-SRS.
[0102] As shown in FIG. 7B, when "AS Enable=0" the transceiver
transmits R-SRS from only one antenna. A total of 2 SRSs are
required in each cycle to sound the entire bandwidth. Based on the
received SRSs, the eNodeB makes scheduling decisions without any
antenna selection.
[0103] Adaptive SRS: FIGS. 8A and 8B show the protocol for hopping
adaptive A-SRS and R-SRS, respectively. As shown in FIG. 8A, upon
receiving the request 801 from the eNodeB, the transceiver sends a
total of 4 SRSs. Based on one or more SRSs, the eNodeB can make AS
and scheduling decisions at any time. In FIG. 8B, because R-SRS is
employed (AS Enable=0), a total of 2 SRSs is sent by the
transceiver for the eNodeB to make scheduling decisions. The
interval between the 2 SRSs is determined by the "Period1"
field.
[0104] Protocol Description for [Option2]
[0105] FIG. 9 shows the legend for protocol [Option2], which is
used for the illustrations from FIG. 10A to FIG. 13B. The legends
are Wideband or variable bandwidth SRS 901, Narrow-band hopping SRS
902, Data block (sub-frame) if no SRS is sent at the same TTI 903,
Data block (sub-frame) if SRS is sent at the same TTI 904, No data
to send in a TTI 905, Level-B slower signaling: SRS parameters,
906, Level-C faster signaling: SRS request (to start) 907, and
Level-C faster signaling: AS & scheduling decision 908. For
clarity Level-A signaling exchange is omitted herein. It should be
noted that all the protocol illustrations provided herein are only
examples.
[0106] Similar to FIGS. 5A to 8B, FIGS. 10A to 13B show the same
SRS scenarios when the signaling is set to [Option2], respectively.
Recall that in [Option2], the Level-B SRS parameters are sent
separately from the Level-C SRS start/stop request. Also, it is
assumed that when the transceiver receives an SRS request, the
transceiver has obtained of the required SRS parameters in a
separate Level-B message (or uses default values for the parameter
values it has not received yet). For instance, as shown in FIG.
10A, the eNodeB can send the SRS parameters 1001 and the SRS
request 1002 at the same TTI. As shown in FIG. 11A, the SRS
parameter 1101 can also be sent before the SRS request 1102. The
other procedures are the same as [Option1].
[0107] Switching Between Different SRS Patterns
[0108] In order to switch between different SRS patterns (e.g.,
periodic vs. adaptive, hopping vs. non-hopping, etc), a Level-B
slower signaling from the eNodeB to the transceiver is required for
both [Option1] and [Option2] to set up different SRS parameters. In
addition, for [Option2], an "SRS Start" from the eNodeB to the
transceiver is also needed.
[0109] It should be noted that under the current protocol, the
eNodeB can possibly send SRS request and the AS decision in the
same TTI. It should also be noted that when the number of hops
(i.e., the "Num_Hops" field in parameter list) is larger than 2,
different hopping patterns that jointly span the frequency-space
domain can be designed. The pattern can be either signaled by the
eNodeB or is chosen from a pre-determined set. In FIGS. 5A to 8B
and FIGS. 10A to 13B, only the procedure of "SRS Start" is shown.
The procedure of "SRS Stop" is not shown in these figures, and is
sent in a similar manner.
[0110] Antenna Selection Protocol for HARQ
[0111] Asynchronous HARQ
[0112] If the system operates in an asynchronous HARQ mode, then
the eNodeB indicates to the transceiver when, which RBs, and with
what MCS (modulation and coding scheme) to retransmit the packet.
Because the eNodeB has complete control over the packet
retransmission in asynchronous HARQ, the eNodeB can also signal the
transceiver whether or not to switch the antenna for
retransmission. It can also indicate to the transceiver to send an
aperiodic or a periodic A-SRS. In this case, the eNodeB makes a
joint AS and scheduling decision for the retransmitted packet,
similar to that for a normal packet.
[0113] Synchronous HARQ
[0114] If the system operates in synchronous HARQ mode, then the
transceiver knows a priori exactly when to retransmit the packet
when it does not receive an ACK from the eNodeB after a
pre-specified number of TTIs. In this case, the transceiver uses
the same resource block (RB) and same MCS for the retransmission.
Because the transceiver has complete control over the packet
retransmission in synchronous HARQ, whenever retransmission occurs,
the transceiver can automatically switch to another subset of
antennas to retransmit (using the same RB and MCS). This is to
avoid the scenario that the channel quality of the previously
selected subset of antennas is poor.
EFFECT OF THE INVENTION
[0115] The embodiments of the invention provide signaling and
protocol for antenna selection in the uplink of OFDM 3GPP wireless
network between the transceiver and the eNodeB.
[0116] Although the invention has been described by way of examples
of preferred embodiments, it is to be understood that various other
adaptations and modifications may be made within the spirit and
scope of the invention. Therefore, it is the object of the appended
claims to cover all such variations and modifications as come
within the true spirit and scope of the invention.
* * * * *