U.S. patent application number 14/501679 was filed with the patent office on 2015-01-15 for antenna selection with frequency-hopped sounding reference signals.
The applicant listed for this patent is Mitsubishi Electric Research Laboratories, Inc.. Invention is credited to Neelesh B Mehta, Man-On Pun, Koon Hoo Teo, Gennadiy Vinokur, Jinyun Zhang.
Application Number | 20150016489 14/501679 |
Document ID | / |
Family ID | 41550672 |
Filed Date | 2015-01-15 |
United States Patent
Application |
20150016489 |
Kind Code |
A1 |
Mehta; Neelesh B ; et
al. |
January 15, 2015 |
Antenna Selection with Frequency-Hopped Sounding Reference
Signals
Abstract
The embodiments of the invention provide a method for selecting
antennas for data transmission in a wireless communication network
including user equipment (UE). The network is assigned a band of
frequencies, wherein the band is partitioned into at least one set
of subbands of the band according to a sounding reference signal
(SRS) bandwidth configuration in a form of a code-tree having a
plurality levels and each level is associated with a partition
coefficient. The UE is configured to transmit frequency-hopped SRS
on the set of subbands using subsets of the set of antennas. First,
the method determines if a number of subbands in the set of the
subbands is odd or even based on the SRS bandwidth configuration,
and selects a particular subset of the antennas according to
whether the number is odd or even. Then, the SRS is transmitted
from the particular subset of the antennas.
Inventors: |
Mehta; Neelesh B;
(Bangalore, IN) ; Teo; Koon Hoo; (Lexington,
MA) ; Zhang; Jinyun; (Cambridge, MA) ;
Vinokur; Gennadiy; (Marblehead, MA) ; Pun;
Man-On; (Cambridge, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Mitsubishi Electric Research Laboratories, Inc. |
Cambridge |
MA |
US |
|
|
Family ID: |
41550672 |
Appl. No.: |
14/501679 |
Filed: |
September 30, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13002295 |
Sep 8, 2011 |
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PCT/US09/48512 |
Jun 24, 2009 |
|
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14501679 |
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Current U.S.
Class: |
375/135 |
Current CPC
Class: |
H01Q 25/00 20130101;
H04B 1/713 20130101; H01Q 3/24 20130101; H04B 7/0602 20130101; H04L
5/0048 20130101; H04W 88/08 20130101; H01Q 1/246 20130101; H04W
88/02 20130101; H04B 7/0691 20130101; H04W 28/16 20130101; H04L
5/0053 20130101; H04L 5/0023 20130101 |
Class at
Publication: |
375/135 |
International
Class: |
H04L 5/00 20060101
H04L005/00; H04W 88/08 20060101 H04W088/08; H04B 7/06 20060101
H04B007/06; H04B 1/713 20060101 H04B001/713 |
Claims
1. A method for selecting antennas for data transmission in a
wireless communication network including user equipment (UE),
wherein the network is assigned a band of frequencies, wherein the
band is partitioned into at least one set of subbands of the band
according to a sounding reference signal (SRS) bandwidth
configuration, wherein the SRS bandwidth configuration is in a form
of a code-tree having a plurality levels and each level is
associated with a partition coefficient, and wherein the UE
includes a set of antennas, and wherein the UE is configured to
transmit frequency-hopped SRS on the set of subbands using subsets
of the set of antennas, comprising in the UE a processor for
performing steps of the method, comprising the steps of:
determining if a number of subbands in the set of the subbands is
odd or even based on the SRS bandwidth configuration; selecting a
particular subset of the antennas according to whether the number
is odd or even; and transmitting the SRS from the particular subset
of the antennas to enable antenna selection for data
transmission.
2. The method of claim 1, wherein the determining further
comprising: selecting partition coefficients based on the SRS
bandwidth configuration; and multiplying the partition coefficients
to produce a product of the partition coefficients, such that the
product equals the number of subbands.
3. The method of claim 1, wherein the number of subbands is odd,
and wherein the selecting further comprising: determining an index
parameter a(nSRS) of the particular subset of antennas according to
a(n.sub.SRS)=n.sub.SRS mod2, wherein nSRS is an index of a
transmission of the SRS.
4. The method of claim 1, wherein the number of subbands is even,
and wherein the selecting further comprising: determining an index
parameter a(nSRS) of the particular subset of antennas according to
a ( n SRS ) = ( n SRS + [ n SRS b = 0 b N b ] mod 2 ) mod 2 ,
##EQU00003## wherein nSRS is an index of a transmission of the SRS,
b is a level of the segments in a code-tree based SRS allocation,
and Nb is a partitioning coefficient of the b level segments.
5. The method of claim 1, wherein the number of subbands is odd,
and a number of subsets in the set of antennas is even, the
selecting further comprising: determining an index parameter
a(nSRS) of the particular subset of antennas according to
a(nSRS)=nSRS mod xa, wherein nSRS is an index of the transmission
of the SRS, and xa is the number of subsets in the set of the
antennas.
6. The method of claim 1, wherein the number of subbands is even,
and a number of subsets in the set of antennas is odd, the
selecting further comprising: determining an index parameter
a(nSRS) of the particular subset of antennas according to
a(nSRS)=nSRS mod xa, wherein nSRS is an index of the transmission
of the SRS, and xa is the number of subsets in the set of the
antennas.
7. The method of claim 1, further comprising: receiving the SRS
bandwidth configuration from a base station.
8. The method of claim 1, further comprising: receiving an index of
the SRS bandwidth configuration from a base station; and selecting
the SRS bandwidth configuration based on the index.
9. The method of claim 1, wherein the transmitting is associated
with an index nSRS of a transmission of the SRS.
10. The method of claim 1, wherein the SRS bandwidth configuration
is determined in part by SRS bandwidths and by SRS hopping
bandwidths.
11. The method of claim 1, wherein the selecting further
comprising: determining an index parameter a(nSRS) of the optimal
subset of antennas according to a(n.sub.SRS)=n.sub.SRS mod2,
wherein nSRS is an index of a transmission of the SRS.
13. A wireless communication network, wherein the network is
assigned a band of frequencies, wherein the band is partitioned in
at least one set of subbands of the band according to a sounding
reference signal (SRS) bandwidth configuration, wherein the SRS
bandwidth configuration is in a form of a code-tree having a
plurality levels, and each level is associated with a partition
coefficient, the network comprising: user equipment (UE), wherein
the UE includes a set of antennas, and wherein the UE is configured
to transmit a frequency-hopped SRS over the set of subbands using
subsets of the set of antennas, and wherein the UE is configured to
select a particular subset of the set of antennas based on whether
a number of subbands in the set of the subbands is odd or even,
wherein the number of the subbands is defined by the SRS bandwidth
configuration.
14. The network of claim 13, wherein the SRS bandwidth
configuration determines partition coefficients, such that a
product of the partition coefficients equals the number of
subbands, and wherein the UE is configured to multiply the
partition coefficients.
15. The network of claim 13, wherein the UE further comprising: a
memory for storing the SRS bandwidth configuration, wherein the SRS
bandwidth configuration is identified by an index; and means for
receiving the index from the base station.
16. The network of claim 13, wherein the UE is further configured
to determine an index parameter a(nSRS) of the particular subset of
antennas according to a(n.sub.SRS)=n.sub.SRSmod2, wherein nSRS is
an index of a transmission of the SRS.
18. A user equipment (UE), comprising: a set of antennas, wherein
the UE is configured to transmit frequency-hopped sounding
reference signal (SRS) using subsets of the set of antennas
according to a SRS bandwidth configuration; means for determining a
number of subbands in the set of the subbands is odd or even,
wherein the numbers of the subbands equals to a product of
partition coefficients defined by the SRS bandwidth configuration;
means for selecting a particular subset of antennas based on the
number of subbands; and means for transmitting the SRS from the
particular subsets of the antennas to select an optimal subset of
antennas for data transmission.
19. The UE of claim 18, further comprising: means for determining
an index parameter a(nSRS) of the optimal subset of antennas
according to a(n.sub.SRS)=n.sub.SRS mod2, wherein nSRS is an index
of a transmission of the SRS.
20. The UE of claim 18, further comprising: means for determining
an index parameter a(nSRS) of the optimal subset of antennas
according to a(nSRS)=nSRS mod xa, wherein nSRS is an index of the
transmission of the SRS, and xa is a number of subsets in the set
of the antennas.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 13/002,295 submitted by Mehta et al. on Sep.
8, 2011 for "Antenna Selection with Frequency-Hopped Sounding
Reference Signals" which in turn is a national stage entry of
PCT/US09/48512, filed on Jun. 24, 2009.
FIELD OF THE INVENTION
[0002] This invention relates generally to antenna selection in
wireless communication networks, and more particularly to selecting
antennas with frequency-hopped sounding reference signals
(SRS).
BACKGROUND OF THE INVENTION
[0003] OFDMA and SC-FDMA
[0004] In a wireless communication network, such as the 3.sup.rd
generation (3G) wireless cellular communication standard and the
3GPP long term evolution (LTE) standard, it is desired to
concurrently support multiple services and multiple data rates for
multiple users in a channel with a fixed bandwidth. The network
bandwidth can vary, for example, from 1.25 MHz to 20 MHz. The
network bandwidth is partitioned into a number of subbands, e.g.,
1024 subbands for a 10 MHz bandwidth.
[0005] One scheme adaptively modulates and encodes symbols, before
transmission, based on estimates of a channel. Another option
available in LTE, which uses orthogonal frequency division
multiplexed access (OFDMA), is to use multi-user frequency
diversity by assigning different subbands or groups of subbands to
different users or UEs (user equipment, mobile station (MS).
[0006] In the single band frequency division multiple access
(SC-FDMA) uplink of the LTE, in each UE, the symbols are spread by
means of a discrete Fourier transform (DFT) matrix. Then, the
symbols are assigned to different subbands.
[0007] The following standards are applicable: 36.211, 3rd
Generation Partnership Project; Technical Specification Group Radio
Access Network; Physical Channels and Modulation (Release 8), v
1.0.0 (2007-03); R1-01057, "Adaptive antenna switching for radio
resource allocation in the EUTRA uplink," Mitsubishi
Electric/Nortel/NTT DoCoMo, 3GPP RAN1#48; R1-071119, "A new DM-RS
transmission scheme for antenna selection in E-UTRA uplink," LGE,
3GPP RAN1#48; and "Comparison of closed-loop antenna selection with
open-loop transmit diversity (antenna switching within a transmit
time interval (TTI))," Mitsubishi Electric, 3GPP RAN1#47bis,
Sorrento, Italy. According to the 3GPP standard, the base station
(BS) is enhanced, and is called the "Evolved NodeB" (eNodeB). The
terms BS and eNodeB are used interchangeably.
[0008] Multiple Input Multiple Output (MIMO)
[0009] To further increase the capacity of the wireless
communication network in fading channel environments,
multiple-input-multiple-output (MIMO) antenna technology can be
used without an increase in bandwidth. Because the channels for
different antennas are different, MIMO decreases fading, and also
enables multiple data streams to be transmitted concurrently.
[0010] However, processing the signals received in spatial
multiplexing schemes, or with space-time trellis codes requires
transceivers where the complexity can increase exponentially as a
function of the number of antenna.
[0011] Antenna Selection
[0012] Antennas are relatively simple and cheap, while RF chains
are considerably more complex and expensive. Antenna selection
reduces some of the complexity drawbacks associated with MIMO
networks. Antenna selection reduces the hardware complexity of
transmitters and receivers in the transceivers by using fewer RF
chains than the number of antennas.
[0013] During antenna selection, a subset of the set of available
antennas is adaptively selected by a switch, and only signals for
the selected subset of antennas are connected to the available RF
chains for signal processing, which can be either transmitting or
receiving. The selected subset can include one or more of the
available antennas.
[0014] Pilot Tones or Reference Signals
[0015] To select the optimal subset of antennas, channels
corresponding to available subsets of antennas need to be
estimated, even though only a selected optimal subset of the
antennas is eventually used for transmission.
[0016] This can be achieved by transmitting antenna selection
signals, e.g., pilot tones, also called sounding reference signals
(SRS), from different antenna subsets. The different antenna
subsets can transmit either the same pilot tones, or use different
pilot tones. Let N.sub.t denote the number of transmit antennas,
N.sub.r the number of receive antennas, and let
R.sub.t=N.sub.t/L.sub.t and R.sub.r=N.sub.r/L.sub.r be integers.
Then, the available transmit (receive) antennas can be partitioned
into R.sub.t (R.sub.r) disjoint subsets.
[0017] The pilot repetition approach repeats, for
R.sub.t.times.R.sub.r times, a training sequence that is suitable
for an L.sub.t.times.L.sub.r MIMO network. During each repetition
of the training sequence, the transmit RF chains are connected to
different subsets of the antennas. Thus, at the end of the
R.sub.t.times.R.sub.r repetitions, the receiver has a complete
estimate of all the channels from the various transmit antennas to
the various receive antennas.
[0018] In case of transmit antenna selection in frequency division
duplex (FDD) networks, in which the forward and reverse channels
are not identical, the transceiver feeds back the optimal subset of
antennas to the transmitter. In reciprocal time division duplex
(TDD) networks, the transmitter can perform the selection
independently.
[0019] For an indoor local area network (LAN) with slowly varying
channels, antenna selection can be performed using a media access
(MAC) layer protocol, see IEEE 802.11n wireless LAN draft
specification, I. P802.11n/D1.0, "Draft amendment to Wireless LAN
media access control (MAC) and physical layer (PHY) specifications:
Enhancements for higher throughput," Tech. Rep., March 2006.
[0020] Instead of extending the physical (PHY) layer preamble to
include the extra training fields (repetitions) for the additional
antennas, antenna selection training is done at the MAC layer by
issuing commands to the physical layer to transmit and receive
packets by different antenna subsets. The training information,
which is a single conventional training sequence for an
L.sub.t.times.L.sub.r MIMO network, is embedded in the MAC header
field.
[0021] SC-FDMA Structure in LTE
[0022] The basic uplink transmission scheme is described in 3GPP TR
25.814, v1.2.2 "Physical Layer Aspects for Evolved UTRA." The
scheme is a single-band transmission (SC-FDMA) with cyclic prefix
(CP) to achieve uplink inter-user orthogonality and to enable
efficient frequency-domain equalization at the receiver.
[0023] Broadband Sounding Reference Signals (SRS)
[0024] The broadband SRS helps the eNodeB to estimate the entire
frequency domain response of the uplink channel from the UE to the
eNodeB. This helps frequency-domain scheduling, in which a subband
is assigned to the UE with the best gain on the uplink channel for
that subband. Therefore, the broadband SRS can use the entire
bandwidth, e.g., 5 MHz or 10 MHz, or a portion thereof as
determined by the eNodeB. In the latter case, the broadband SRS is
frequency hopped over multiple transmissions to cover the entire
network bandwidth.
SUMMARY OF THE INVENTION
[0025] The embodiments of the invention describe a method for
selecting antennas for data transmission in a wireless
communication network including user equipment (UE). The network is
assigned a band of frequencies, wherein the band is partitioned
into at least one set of subbands of the band according to a
sounding reference signal (SRS) bandwidth configuration in a form
of a code-tree having a plurality levels and each level is
associated with a partition coefficient. The UE is configured to
transmit frequency-hopped SRS on the set of subbands using subsets
of the set of antennas. First, the method determines if a number of
subbands in the set of the subbands is odd or even based on the SRS
bandwidth configuration, and selects a particular subset of the
antennas according to whether the number is odd or even. Then, the
SRS is transmitted from the particular subset of the antennas.
[0026] The execution of the method depends on whether a value of
the product is odd or even. In one embodiment, the number of
subbands is odd, and the method determines an index parameter
a(n.sub.SRS) of the particular subset of antennas according to
a(n.sub.SRS)=n.sub.SRS mod 2 , wherein n.sub.SRS is an index of a
transmission of the SRS.
[0027] In another embodiment, the number of subbands is even, and
the method determines the index parameter of the particular subset
of antennas according to
a ( n SRS ) = ( n SRS + [ n SRS b = 0 b N b ] mod 2 ) mod 2 ,
##EQU00001##
wherein b is a level of the segments in a code-tree based SRS
allocation, and N.sub.b is a partitioning coefficient of the b
level segments.
[0028] In yet another embodiment, the number of subbands is odd,
and a number of subsets in the set of antennas is even, and the
method determines the index parameter of the particular subset of
antennas according to
[0029] a(n.sub.SRS)=n.sub.SRS mod x.sub.a, wherein x.sub.a is the
number of subsets in the set of the antennas.
[0030] In alternative embodiment, the number of subbands is even,
and a number of subsets in the set of antennas is odd, and the
method determines the index parameter of the particular subset of
antennas according to
a(n.sub.SRS)=n.sub.SRS mod x.sub.a.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] FIG. 1A is a block diagram of a wireless network according
to an embodiment of the invention;
[0032] FIG. 1B is a block diagram of user equipment according to an
embodiment of the invention;
[0033] FIG. 2 is a block diagram of an uplink resource grid
according to an embodiment of the invention;
[0034] FIG. 3A is a block diagram of a frame according to an
embodiment of the invention;
[0035] FIG. 3B is a block diagram of a resource block according to
an embodiment of the invention;
[0036] FIG. 4 is a block diagram of method for selecting antennas
according to an embodiment of the invention;
[0037] FIG. 5 and FIG. 6 are block diagrams of a frequency-hopped
sounding reference signal (SRS) transmissions;
[0038] FIG. 7 is a block diagram of a method and a network for
training subsets of antennas with the frequency-hopped SRS
according to embodiments of the invention;
[0039] FIG. 8 and FIG. 9 are block diagrams of a frequency-hopped
sound reference signal (SRS) transmission patterns according to
embodiments of the invention;
[0040] FIG. 10 is a schematic of hopping patterns according to a
code-tree based SRS allocation;
[0041] FIG. 11 is a block diagram of an example of the SRS
bandwidth configuration;
[0042] FIG. 12 is a block diagram of an example of the SRS
bandwidth configuration using a tree data structure according
embodiments of the invention;
[0043] FIG. 13 is a block diagram of a method for selecting optimal
subset of antennas from the set of antennas according embodiments
of the invention; and
[0044] FIG. 14 is a block diagram of a method for selecting optimal
subset of antennas from the set of antennas, which include
arbitrarily number of subsets of antennas according another
embodiment of the invention .
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0045] Network Overview
[0046] FIG. 1A shows a general structure of a wireless network
according to an embodiment of the invention. In one embodiment, the
network operates according the 3GPP long term evolution standard
(LTE). Multiple mobile user equipments (UEs) 111-113 communicate
with a stationary base station (BS) 110. Each UE and the BS
includes a transceiver.
[0047] The BS is called an evolved Node B (eNodeB) in the LTE
standard. The BS manages and coordinates all communications with
the UEs in a cell using wireless channels or connections 101, 102,
103. Each connection can operate as a downlink (DL) 107 from the BS
station to the UE or as an uplink 108 from the UE to the BS.
Because the transmission power available at the BS is orders of
magnitude greater than the transmission power at the UE, the
performance on the uplink is much more critical.
[0048] FIG. 1B is a block diagram of detail of UE 120. The UE
includes a processor for performing steps of the method described
herein. The processor 121 connected to a RF transmitter 121 and a
RF receiver 121. The processor includes a memory 125. The
transmitter and the receiver are connected to a set of antennas 124
via a switch, so one or more antennas can either transmit or
receive signals. As shown, the switch is configured to
transmit.
[0049] To perform wireless communication, the BS and the UEs are
equipped with at least one RF chain and a set of antennas.
Normally, the number of antennas and the number RF chains are equal
at the BS. The number of antennas at the BS can be quite large,
e.g., eight or more. However, due to the limitation on cost, size,
and power consumption, UEs usually have fewer antennas 115, e.g.,
two or four. Therefore, antenna training and selection is performed
at the UEs.
[0050] Generally, antennas selection selects a subset of antennas
from the set of available antennas at the UE. The antennas
selection includes the training, which is used for generating and
transmitting and receiving antenna selection signals. The
embodiments of the invention enable the network to accommodate UEs
different bandwidths for sounding reference signals (SRS) in an
orthogonal manner, and use the limited resource of the SRS.
[0051] LTE Frame Structure
[0052] As shown in FIG. 3A, transmissions on the uplink and
downlink are organized into frames 299. Each frame includes a
downlink subframe 301 and an uplink subframe 302. Each frame is 10
ms, and includes of 20 slots of 0.5 ms each.
[0053] FIG. 2 shows the structure of a SC-FDMA (single band
frequency division multiple access) uplink resource grid 200. The
horizontal axis indicates time, or SC-FDMA symbols and the vertical
axis indicates frequency or subbands. The number of subbands
depends on the bandwidth of the network, which can range from 1.25
MHz to 20 MHz, for example.
[0054] The uplink resource grid includes resource elements. Each
resource element is indentified by the subband 220 and the SC-FDMA
symbol 210. The resource elements are grouped into resource blocks.
A resource block (RB) 300 includes of 12 consecutive subbands and
six or seven consecutive SC-FDMA symbols. The number of SC-FDMA
symbols depends on a length of a cyclic prefix (CP). For a normal
cyclic prefix, the number of SC-FDMA symbols is 7 and for an
extended cyclic prefix, the number of SC-FDMA symbols is 6.)
[0055] For the purpose of this specification and appended claims,
we use the terms the subframe and the transmission time interval
(TTI) interchangeably.
[0056] FIG. 3B shows a structure of the resource block (RB) 300
with a conventional cyclic prefix. The vertical axis indicates
frequency, and the horizontal axis indicates time. In the frequency
domain, the resource block includes of a number of subbands. In the
time domain, the RB is partitioned into SC-FDMA symbols, which may
include data 303 and reference signals (RS) 310. Two types of the
RS are used in the uplink: sounding reference signals (SRS) 311 and
demodulation reference signals (DMRS) 310.
[0057] Both the SRS and the DMRS are generated using a constant
amplitude zero autocorrelation sequence (CAZAC) sequence, such as a
Zadoff-Chu sequence, as described in Section 5.5.1 of the TS 36.211
v8.5.0 standard. When the sequence length is not equal to the
length possible for a Zadoff-Chu sequence, the sequence of desired
length is generated by extending circularly a Zadoff-Chu sequence
of length close to and less than the desired length, or by
truncating a Zadoff-Chu sequence of length close to and greater
than the desired length. The DMRS is transmitted in the fourth
SC-FDMA symbol for normal cyclic prefix and in the third SC-FDMA
symbol for the extended cyclic prefix. The SRS is typically
transmitted in the last SC-FDMA symbol of the subframe, except for
special subframes as described in TS 36.211 v8.5.0. However, the
embodiments of the invention do not depend on the SC-FDMA symbol in
which the RS is transmitted.
[0058] Antennas Selection
[0059] Typically, the RS is transmitted along with or separately
from user data from different subsets of antennas. Based on the
RSs, the BS, estimates channels and identifies the optimal subset
of antennas for data transmission.
[0060] FIG. 4 shows the basic method for selecting antennas
according to an embodiment of the invention. The base station 110
specifies 150 instructions 151, e.g., frequency-hopped pattern and
subsets of antennas to use for transmitting the RSs 161. The
transmitter of the UE 101 transmits 160 the RSs 161 according to
the instructions 151.
[0061] The BS selects 170 a subset of antennas 181 based on the
received RSs. Then, the BS indicates 180 the selected subset of
antenna 181 to the UE. Subsequently, the UE transmits 190 data 191
using the selected subset of antennas 181. The UE can also use the
same subset of antennas for receiving transmitting data.
[0062] Sounding Reference Signal (SRS)
[0063] The SRS is usually a wideband or variable bandwidth signal.
The SRS enables the BS to estimate a frequency response of the
entire bandwidth, or only a portion thereof The frequency response
enables the BS to allocate resources such as uplink
frequency-domain scheduling. According to the embodiment of the
invention, the SRSs are also used for antenna selection.
[0064] Another option for LTE is to use a frequency-hopping (FH)
pattern to transmit the SRS. Specifically, a hopping SRS, with a
subband, is transmitted based on a pre-determined frequency hopping
pattern. The hopped SRSs, over multiple transmissions, span a large
portion of the entire bandwidth, or the entire available bandwidth.
With frequency hopping, the probability that UE interfere with each
other during training is decreased.
[0065] However, if the antenna selection is performed incorrectly,
the frequency-hopped variable bandwidth SRS results in a small
performance improvement, particularly if the UE is moving
rapidly.
[0066] As shown in FIG. 5, all the subbands of antenna Tx.sub.1 are
successively sounded by the frequency-hopped SRS. Then, the
subbands of antenna Tx.sub.2 are successively sounded in a similar
manner, as shown by the shaded blocks. However, the channel
estimates obtained from this frequency-domain antenna selection
pattern is quickly outdated. For example, at the end of sounding
with antenna Tx.sub.2, the channel estimates for antenna Tx.sub.1
may no longer be valid.
[0067] FIG. 6 shows subframes with frequency-hopped SRS transmitted
alternately from the subsets of antennas. For example, the UE
transmits the SRS alternately from two subsets of antennas, i.e.,
Tx.sub.1 210 and Tx.sub.2 220. The available bandwidth 240 is
partitioned into four subbands 241-244, such that the SRS covers
the bandwidth with four transmissions 250. The subband can occupy
one or multiple RBs.
[0068] In this training scenario, the SRSs for the subbands 241 and
243 are always transmitted from the subset of antennas Tx.sub.1,
and the SRSs for the subbands 242 and 244 are always transmitted
from the subset of antennas Tx.sub.2. Hence, the UE is not able to
estimate the channel over entire frequency domain for each
available subset of antennas.
[0069] Transmitting substantially alternately means that the
alternating schedule changes over time. We assign an index for each
subset of antennas, and antennas can be `selected` or `unselected.`
For example, if the transceiver has two subsets of antennas, then
the indexes are 0 and 1. The index pattern is [0, 1, 0, 1, 0, 1, 0,
1 . . . ], and [0, 1, 2, 0, 1, 2, 0, 1, 2, 0, 1, 2 . . . ] for
three subsets.
[0070] Transmitting substantially alternately leads to an index
pattern, e.g., [0, 1, 0, 1, 1, 0, 1, 0, 0, 1 . . . ]. For the
transmitting substantially alternately, we periodically alter the
index for the transmitting subset, e.g., shift or omit the
indexes.
[0071] The index of the selected subset of antennas a(n.sub.SRS)
depends on the subframe number n.sub.SRS in which the SRS is
transmitted and the number of the subset of antennas. Therefore,
the index pattern above can be specified in the form of a
functional relationship between a(n.sub.SRS) and n.sub.SRS, The
functional relationship depends on other parameters such as, but
not limited to, the BS index and the length of the SRS
sequence.
[0072] FIG. 7 shows a method 700 for training for the subset of
antennas. We determine 740 a type of a transmission based on a
relationship between the number of subbands 710 and the number of
the subsets of transmit antennas 720. We determine whether the
number of subbands is integer multiplier of the number of transmit
antennas. If true 731, we transmit 760 the SRSs substantially
alternately 760. For example, we alter an antenna index 750 every
time when the end of the bandwidth is reached 735. In alternative
embodiment, we alter the antenna index after the end or at the
beginning of the frequency-hopped pattern. If false 730, we
transmit the SRSs alternately.
[0073] FIG. 8 shows a pattern for transmitting alternately the
frequency-hopped SRS. The available bandwidth of B Hz 810 is
partitioned into N.sub.f 830 subbands of bandwidth B/N.sub.f Hz
each. If the number of subbands is odd, and the number of the
subsets of antennas is even, then the number of subbands is not
integer multiplier of the number of transmit antennas and the
transmission from the two antennas Tx1 and Tx2 alternately results
in a time-interleaved frequency hopping pattern 820.
[0074] FIG. 9 shows another pattern. There are four subbands and
two antennas. When the transmission reaches the end of the
bandwidth, e.g., a pattern of transmissions 920, we alter the
indexes of the subset of the antennas. Thus, the next pattern of
transmissions 930 starts with the subset of antennas Tx.sub.2.
[0075] In one embodiment, the decision of which training pattern to
use is made by the BS. The training pattern is transmitted to the
UE as part of the instruction 151. In alternative embodiment, the
UE has prior knowledge of the possible training patterns, and the
instruction 151 only identifies the training pattern to use.
[0076] Frequency-Hopped SRS
[0077] Some embodiments of the invention use a subset of antennas
index a(n.sub.SRS) to allow the UEs to transmit over the entire
bandwidth without interfering with each other. It is often desired
to accommodate multiple UEs with different SRS bandwidths. By
employing frequency-hopping with a code-tree based SRS
configuration, multiple UEs are enabled to transmit orthogonal SRS
with different bandwidths. According to some embodiments, n.sub.SRS
is an index of transmission of the SRS, e.g., time or transmission
order number index, which is used to select the optimal subset of
antennas.
[0078] FIG. 10 shows an example hopping patterns according to a
code-tree based SRS allocation. The code-tree based SRS
configuration is determined, in part, by the SRS bandwidth
B.sub.SRS 1010 and by SRS hopping bandwidth b.sub.hop 1020. The SRS
bandwidth B.sub.SRS depends on a level b 1015 of the code-tree
1030, e.g., b=0, 1, 2, and 3.
[0079] Different values of the SRS hopping bandwidth b.sub.hop
typically lead to different code-tree based SRS bandwidth
configurations 1021-1024. When the SRS hopping bandwidth is less
than or equal to the SRS bandwidth, the frequency-hopping is
disabled, as shown in the configuration 1024.
[0080] FIG. 11 shows a code-tree based SRS bandwidth configuration.
For every level b of the tree, the available bandwidth 1110, e.g.,
an uplink bandwidth N.sub.RB.sup.UL, is partitioned into a number
of subbands. For example, the SRS bandwidth configuration of level
3, B.sub.SRS=3, partitions the bandwidth 1110 into 8 subbands 1120.
Typically, the available bandwidth is represented in a root node
1110 of the tree 1100.
[0081] The structure of the tree 1100 is similar to complete n-ary
tree. The tree has a single root node 1110, intermediate nodes
1130, 1140 and 1150 that have children node, and leaf nodes 1120
that do not have children. The number of children n 1105 at a
particular level is constant, but can vary among different levels.
For example, the root node 1110 has one child, i.e., the node 1130.
Accordingly, the number of children n equals 1. The node 1140 has
two children, i.e., nodes 1150 and 1153. Accordingly, the number of
children n equals 2. That also means that all siblings of the node
1140 should also have exactly two children. For example, a node
1145 has two children, i.e., nodes 1157 and 1159.
[0082] The structure of the tree 1100 can be used to determine a
number of nodes in the level b of the tree by multiplying numbers n
1105 for each level from 0 to b. For example, according to the FIG.
11, the number of nodes at the level 2 (b=2) is
1.times.2.times.2=4. Similarly, number of leaf nodes 1120 at the
level 3 1120 is 1.times.2.times.2.times.2=8.
[0083] The code-tree based SRS configuration utilizes the structure
of the tree 1100. The SRS bandwidth configuration includes a
partitioning coefficient N.sub.b, which is an analogous of the
number of children n 1105. The partitioning coefficient N.sub.b
indicates a number of the b.sup.th level subbands derived from a
(b-1).sup.th level subband. The SRS bandwidth configuration also
includes a number of resource blocks (RB) m.sub.SRS,b in one
subband N.sub.b.
[0084] FIG. 12 shows an example of the SRS bandwidth configuration.
For example, the SRS bandwidth B.sub.SRS=2, which corresponds to a
third, i.e., b=2, level of the code-tree 1100 is partitioned into
two subbands 1220 and 1221, i.e., the partition coefficient
N.sub.b=2. Accordingly, knowing the partition coefitients for all
levels of the tree allows for calculation of numbers of the
subbands for any level of the tree. Hence, the SRS bandwidth
configuration usually provide the partition coefficient N.sub.b for
all levels of the tree b.
[0085] For example, in the SRS bandwidth configuration of FIG. 12,
the partition coefficients for levels 0-3 are 1, 2, 2, and 2. Thus,
the number of subbands at, e.g., level 3, is a product of the
multiplication of different values of N.sub.b, i.e.,
1.times.2.times.2.times.2=8. Several example SRS bandwidth
configurations are described in Tables 1-5 of Appendix A.
[0086] Usualy, the BS determines the SRS bandwidth configuration.
In some embodiments, the SRS bandwidth configuration is identified
by an index C.sub.SRS, and the UEs are configured to select the SRS
bandwidth configuration based on the index. In one embodiment, the
UE stores the SRS bandwidth configuration identified by the index.
The UE also receives the index from the BS. In these embodiments,
the UE selects a particular subset of antennas based on the SRS
bandwidth configuration.
[0087] As shown in FIG. 13, for an odd product 1350 produced by the
multiplication 1330 of the partitioning coefficients 1345 defined
by the SRS bandwidth configuration 1340, the method selects 1355 a
subset of antennas 1310 for SRS transmission 1320. For an even
product the method selects 1355 the antenna subset 1311.
[0088] The products 1350 and 1360 match the number of the subbands
of the available bandwidth 1110. The SRS transmission is used by
the BS to select 1370 the optimal subset of antennas for data
transmission.
[0089] Usually, the antenna subsets 1310 and 1311 include multiple
subsets of antennas. In one embodiment, the product is odd 1350,
and the index parameter a(n.sub.SRS) 1355 of the particular subset
of antennas is
a(n.sub.SRS)=n.sub.SRS mod 2, (1)
wherein n.sub.SRS is an index of the transmission of the SRS, i.e.,
counts, e.g., 0, 1, 2 . . . , the number of SRS transmissions.
[0090] In alternative embodiment, the product 1360 is even, and
then the index parameter a(n.sub.SRS) 1265 of the particular subset
of antennas is
a ( n SRS ) = ( n SRS + [ n SRS b = 0 b N b ] mod 2 ) mod 2 , ( 2 )
##EQU00002##
wherein n.sub.SRS is an index of a transmission of the SRS, b is a
level of the code-tree based SRS configuration, and N.sub.b is the
partitioning coefficient of the b.sup.th level of the code-tree
based SRS configuration.
[0091] FIG. 14 shows a block diagram of a method for selecting
optimal subset of antennas from the set of antennas 1410, which
include arbitrarily number of subsets of antennas x.sub.a. If the
product produced by the multiplication 1330 of the partition
coefficients 1345 is odd 1350 and the number of subsets of antennas
x.sub.a is even 1430, or, alternatively, the product is even 1360,
but the number of subsets of antennas x.sub.a is odd 1420, the
index parameter a(n.sub.SRS) 1440 of the particular subset of
antennas is
a(n.sub.SRS)=n.sub.SRS mod x.sub.a ,(3)
wherein n.sub.SRS is an index of the transmission of the SRS, and
x.sub.a is the number of subsets in the set of the antennas.
[0092] 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.
Appendix A
TABLE-US-00001 [0093] TABLE 1 m.sub.SRS,b and N.sub.b, b = 0, 1, 2,
3, values for the uplink bandwidth of 6 .ltoreq. N.sub.RB.sup.UL
.ltoreq. 40. SRS SRS- SRS- SRS- SRS- bandwidth Bandwidth Bandwidth
Bandwidth Bandwidth configuration B.sub.SRS = 0 B.sub.SRS = 1
B.sub.SRS = 2 B.sub.SRS = 3 C.sub.SRS m.sub.SRS,b N.sub.b
m.sub.SRS,b N.sub.b m.sub.SRS,b N.sub.b m.sub.SRS,b N.sub.b 0 36 1
12 3 4 3 4 1 1 32 1 16 2 8 2 4 2 2 24 1 4 6 4 1 4 1 3 20 1 4 5 4 1
4 1 4 16 1 4 4 4 1 4 1 5 12 1 4 3 4 1 4 1 6 8 1 4 2 4 1 4 1 7 4 1 4
1 4 1 4 1
TABLE-US-00002 TABLE 2 m.sub.SRS,b and N.sub.b, b = 0, 1, 2, 3,
values for the uplink bandwidth of 40 < N.sub.RB.sup.UL .ltoreq.
60. SRS SRS- SRS- SRS- SRS- bandwidth Bandwidth Bandwidth Bandwidth
Bandwidth configuration B.sub.SRS = 0 B.sub.SRS = 1 B.sub.SRS = 2
B.sub.SRS = 3 C.sub.SRS m.sub.SRS,0 N.sub.0 m.sub.SRS,1 N.sub.1
m.sub.SRS,2 N.sub.2 m.sub.SRS,3 N.sub.3 0 48 1 24 2 12 2 4 3 1 48 1
16 3 8 2 4 2 2 40 1 20 2 4 5 4 1 3 36 1 12 3 4 3 4 1 4 32 1 16 2 8
2 4 2 5 24 1 4 6 4 1 4 1 6 20 1 4 5 4 1 4 1 7 16 1 4 4 4 1 4 1
TABLE-US-00003 TABLE 3 m.sub.SRS,b and N.sub.b, b = 0, 1, 2, 3,
values for the uplink bandwidth of 60 < N.sub.RB.sup.UL .ltoreq.
80. SRS SRS- SRS- SRS- SRS- bandwidth Bandwidth Bandwidth Bandwidth
Bandwidth configuration B.sub.SRS = 0 B.sub.SRS = 1 B.sub.SRS = 2
B.sub.SRS = 3 C.sub.SRS m.sub.SRS,0 N.sub.0 m.sub.SRS,1 N.sub.1
m.sub.SRS,2 N.sub.2 m.sub.SRS,3 N.sub.3 0 72 1 24 3 12 2 4 3 1 64 1
32 2 16 2 4 4 2 60 1 20 3 4 5 4 1 3 48 1 24 2 12 2 4 3 4 48 1 16 3
8 2 4 2 5 40 1 20 2 4 5 4 1 6 36 1 12 3 4 3 4 1 7 32 1 16 2 8 2 4
2
TABLE-US-00004 TABLE 4 m.sub.SRS,b and N.sub.b, b = 0, 1, 2, 3,
values for the uplink bandwidth of 80 < N.sub.RB.sup.UL .ltoreq.
110. SRS SRS- SRS- SRS- SRS- bandwidth Bandwidth Bandwidth
Bandwidth Bandwidth configuration B.sub.SRS = 0 B.sub.SRS = 1
B.sub.SRS = 2 B.sub.SRS = 3 C.sub.SRS m.sub.SRS,0 N.sub.0
m.sub.SRS,1 N.sub.1 m.sub.SRS,2 N.sub.2 m.sub.SRS,3 N.sub.3 0 96 1
48 2 24 2 4 6 1 96 1 32 3 16 2 4 4 2 80 1 40 2 20 2 4 5 3 72 1 24 3
12 2 4 3 4 64 1 32 2 16 2 4 4 5 60 1 20 3 4 5 4 1 6 48 1 24 2 12 2
4 3 7 48 1 16 3 8 2 4 2
* * * * *