U.S. patent number 9,270,435 [Application Number 13/890,678] was granted by the patent office on 2016-02-23 for sounding reference signal (srs) usage.
This patent grant is currently assigned to NOKIA SOLUTIONS AND NETWORKS OY. The grantee listed for this patent is Nokia Siemens Networks Oy. Invention is credited to Kari Juhani Hooli, Jari Olavi Lindholm, Timo Erkki Lunttila, Esa Tapani Tiirola.
United States Patent |
9,270,435 |
Lindholm , et al. |
February 23, 2016 |
Sounding reference signal (SRS) usage
Abstract
Systems, methods, apparatuses, and computer program products for
controlling sounding reference signal (SRS) transmission are
provided. One method includes incorporating into an uplink grant
message, by a base station in a communications system, information
on whether a last symbol of an uplink subframe is used for physical
uplink shared channel (PUSCH), for sounding reference signal (SRS),
or is empty. The method may then include transmitting the uplink
grant message comprising the information on the last symbol to a
user equipment (UE).
Inventors: |
Lindholm; Jari Olavi (Palojoki,
FI), Lunttila; Timo Erkki (Espoo, FI),
Tiirola; Esa Tapani (Kempele, FI), Hooli; Kari
Juhani (Oulu, FI) |
Applicant: |
Name |
City |
State |
Country |
Type |
Nokia Siemens Networks Oy |
Espoo |
N/A |
FI |
|
|
Assignee: |
NOKIA SOLUTIONS AND NETWORKS OY
(Espoo, FI)
|
Family
ID: |
50478821 |
Appl.
No.: |
13/890,678 |
Filed: |
May 9, 2013 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20140334390 A1 |
Nov 13, 2014 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04L
5/005 (20130101); H04L 5/0053 (20130101); H04L
5/0007 (20130101) |
Current International
Class: |
H04L
5/00 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2 536 047 |
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Dec 2012 |
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EP |
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2 538 738 |
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Dec 2012 |
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EP |
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2 660 992 |
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Nov 2013 |
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EP |
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2011/102768 |
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Aug 2011 |
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WO |
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WO 2011/102768 |
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Aug 2011 |
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WO |
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2012/088876 |
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Jul 2012 |
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WO |
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2013/025147 |
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Feb 2013 |
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WO |
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Other References
International Search Report application No. PCT/EP2014/056241 dated
Jun. 23, 2014. cited by applicant .
3GPP TSG RAN WG1 Meeting #72, "TR skeleton for small cell
enhancements--physical layer aspects", Jan. 28-Feb. 1, 2013, St.
Julian's, Malta, R1-130019. cited by applicant .
3GPP TSG-RAN Meeting #58, "New Study Item Proposal for Small Cell
Enhancements for E-UTRA and E-UTRAN--Physical-layer Aspects", Dec.
4-7, 2012, Barcelona, Spain, RP-122032. cited by applicant .
"3rd Generation Partnership Project; Technical Specification Group
Radio Access Network; Small Cell Enhancements for E-UTRA and
E-UTRAN--Physical Layer Aspects" (Release 12), 3GPP TR 36.8xy,
V0.0.1 (Jan. 2013). cited by applicant .
"3rd Generation Partnership Project; Technical Specification Group
Radio Access Network; Small Cell Enhancements for E-UTRA and
E-UTRAN--Physical Layer Aspects" (Release 12), 3GPP TR 36.872,
V12.1.0 (Dec. 2013). cited by applicant.
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Primary Examiner: Ghowrwal; Omar
Attorney, Agent or Firm: Squire Patton Boggs (US) LLP
Claims
We claim:
1. A method, comprising: incorporating into an uplink grant message
for a physical uplink shared channel (PUSCH), by a base station in
a communications system, information on whether a last symbol of an
uplink subframe that is reserved by the base station in every
n.sup.th subframe for sounding reference signal (SRS)
transmissions, is available for the PUSCH; and transmitting the
uplink grant message comprising the information on the last symbol
to a user equipment (UE), wherein the user equipment is configured
to ignore cell-specific SRS subframe configuration when determining
whether the last symbol of the uplink subframe is available for
transmission of the PUSCH.
2. The method according to claim 1, wherein the information
comprises a new SRS trigger type.
3. The method according to claim 1, wherein the incorporating
further comprises: incorporating one bit in the uplink grant
message to indicate whether the last symbol is available for the
PUSCH, and incorporating one bit in the uplink grant message to
indicate whether the UE should send an SRS.
4. A method, comprising: incorporating into an uplink grant message
by a base station in a communications system, information on
whether a last symbol of an uplink subframe for sounding reference
signal (SRS) transmissions, is available for a physical uplink
shared channel (PUSCH); transmitting the uplink grant message
comprising the information on the last symbol to a user equipment
(UE); and incorporating one bit in the uplink grant message to
indicate whether the last symbol is available for the PUSCH, and
incorporating one bit in the uplink grant message to indicate
whether the UE should send an SRS, wherein said one bit indicating
whether the last symbol is available for the PUSCH and said one bit
indicating whether the UE should send an SRS are interpreted
jointly according to: `00` indicates to not transmit an SRS, and
puncture the PUSCH; `01` indicates to not transmit an SRS, and
transmit the PUSCH in the last symbol; `10` indicates to transmit
an SRS, and puncture the PUSCH; `11` indicates to transmit an SRS,
and transmit the PUSCH.
5. A method, comprising: incorporating into an uplink grant message
by a base station in a communications system, information on
whether a last symbol of an uplink subframe for sounding reference
signal (SRS) transmissions, is available for a physical uplink
shared channel (PUSCH); transmitting the uplink grant message
comprising the information on the last symbol to a user equipment
(UE); and incorporating one bit in the uplink grant message to
indicate whether the last symbol is available for the PUSCH, and
incorporating one bit in the uplink grant message to indicate
whether the UE should send an SRS, wherein a first and a second SRS
configuration are provided, and wherein said one bit indicating
whether the last symbol is available for the PUSCH and said one bit
indicating indicate whether the UE should send an SRS are
interpreted jointly according to: `00` indicates to not transmit an
SRS, and puncture the PUSCH; `01` indicates to not transmit an SRS,
and transmit the PUSCH in the last symbol; `10` indicates to
transmit a first SRS configuration, and puncture the PUSCH; `11`
indicates to transmit a second SRS configuration, and puncture the
PUSCH.
6. The method according to claim 1, wherein the incorporating
further comprises: incorporating two bits in the uplink grant
message to indicate whether the last symbol is available for the
PUSCH.
7. A method, comprising: incorporating into an uplink grant message
by a base station in a communications system, information on
whether a last symbol of an uplink subframe for sounding reference
signal (SRS) transmissions, is available for a physical uplink
shared channel (PUSCH); transmitting the uplink grant message
comprising the information on the last symbol to a user equipment
(UE); and incorporating two bits in the uplink grant message to
indicate whether the last symbol is available for the PUSCH;
wherein the two bits in the uplink grant message indicating whether
the last symbol is available for the PUSCH are interpreted
according to: `00` indicates to puncture the PUSCH in the last
symbol; `01` indicates to transmit part of allocated PUSCH physical
resource blocks (PRBs); `10` indicates to transmit another part of
allocated PUSCH PRBs; `11` indicates to transmit the PUSCH.
8. The method according to claim 2, wherein a new SRS trigger type
has a higher priority than existing SRS trigger types.
9. The method according to claim 1, further comprising defining a
zero-power SRS configuration to allow for flexible muting of the
last symbol.
10. The method according to claim 2, wherein, when use of a new SRS
trigger type is configured, hybrid automatic repeat request (HARQ)
re-transmissions follow a pre-defined codepoint of the new SRS
trigger type or follow puncturing rules defined for an overlapping
cell-specific SRS.
11. An apparatus, comprising: at least one processor; and at least
one memory comprising computer program code, the at least one
memory and the computer program code, with the at least one
processor, causing the apparatus at least to incorporate into an
uplink grant message for a physical uplink shared channel (PUSCH),
information on whether a last symbol of an uplink subframe that is
reserved by a base station in every n.sup.th subframe for sounding
reference signal (SRS) transmissions, is available for the PUSCH;
and transmit the uplink grant message comprising the information on
the last symbol to a user equipment (UE), wherein the user
equipment is configured to ignore cell-specific SRS subframe
configuration when determining whether the last symbol of the
uplink subframe available for transmission of the PUSCH.
12. The apparatus according to claim 11, wherein the information
comprises a new SRS trigger type.
13. The apparatus according to claim 11, wherein the at least one
memory and the computer program code are further configured, with
the at least one processor, to cause the apparatus at least to:
incorporate one bit in the uplink grant message to indicate whether
the last symbol is available for the PUSCH, and incorporating one
bit in the uplink grant message to indicate whether the UE should
send an SRS.
14. The apparatus according to claim 13, wherein said one bit
indicating whether the last symbol is available for the PUSCH and
said one bit indicating whether the UE should send an SRS are
interpreted jointly according to: `00` indicates to not transmit an
SRS, and puncture the PUSCH; `01` indicates to not transmit an SRS,
and transmit the PUSCH in the last symbol; `10` indicates to
transmit an SRS, and puncture the PUSCH; `11` indicates to transmit
an SRS, and transmit the PUSCH.
15. The apparatus according to claim 13, wherein a first and a
second SRS configuration are provided, and wherein said one bit
indicating whether the last symbol is available for the PUSCH and
said one bit indicating indicate whether the UE should send an SRS
are interpreted jointly according to: `00` indicates to not
transmit an SRS, and puncture the PUSCH; `01` indicates to not
transmit an SRS, and transmit the PUSCH in the last symbol; `10`
indicates to transmit a first SRS configuration, and puncture the
PUSCH; `11` indicates to transmit a second SRS configuration, and
puncture the PUSCH.
16. The apparatus according to claim 11, wherein the at least one
memory and the computer program code are further configured, with
the at least one processor, to cause the apparatus at least to:
incorporate two bits in the uplink grant message to indicate
whether the last symbol is available for the PUSCH.
17. The apparatus according to claim 16, wherein the two bits in
the uplink grant message indicating whether the last symbol is
available for the PUSCH are interpreted according to: `00`
indicates to puncture the PUSCH in the last symbol; `01` indicates
to transmit part of allocated PUSCH physical resource blocks
(PRBs); `10` indicates to transmit another part of allocated PUSCH
PRBs; `11` indicates to transmit the PUSCH.
18. The apparatus according to claim 12, wherein a new SRS trigger
type has a higher priority than existing SRS trigger types.
19. The apparatus according to claim 11, wherein the at least one
memory and the computer program code are further configured, with
the at least one processor, to cause the apparatus at least to:
define a zero-power SRS configuration to allow for flexible muting
of the last symbol.
20. The apparatus according to claim 12, wherein, when use of a new
SRS trigger type is configured, hybrid automatic repeat request
(HARQ) re-transmissions follow a pre-defined codepoint of the new
SRS trigger type or follow puncturing rules defined for an
overlapping cell-specific SRS.
21. The apparatus according to claim 11, wherein the apparatus
comprises an evolved node B (eNB).
22. A computer program, embodied on a non-transitory computer
readable medium, the computer program when executed by a processor,
causes the processor to: incorporate into an uplink grant message
for a physical uplink shared channel (PUSCH) information on whether
a last symbol of an uplink subframe that is reserved by a base
station in every n.sup.th subframe for sounding reference signal
(SRS) transmissions, is available for the PUSCH; and transmit the
uplink grant message comprising the information on the last symbol
to a user equipment, wherein the user equipment is configured to
ignore cell-specific SRS subframe configuration when determining
whether the last symbol of the uplink subframe is available for
transmission of the PUSCH.
23. A method, comprising: receiving, by a user equipment, an uplink
grant message for a physical uplink shared channel (PUSCH)
comprising information indicating whether a last symbol of an
uplink subframe that is reserved by a base station in every
n.sup.th subframe for sounding reference signal (SRS)
transmissions, is available for the PUSCH; and determining from the
received information whether the last symbol is available for the
PUSCH; wherein the user equipment is configured to ignore cell
specific SRS subframe configuration when determining whether the
last symbol of the uplink subframe is available for transmission of
the PUSCH.
24. The method according to claim 23, wherein one bit in the uplink
grant message indicates whether the last symbol is available for
the PUSCH, and another bit in the uplink grant message indicates
whether the user equipment should send an SRS.
25. A method, comprising: receiving, by a user equipment, an uplink
grant message comprising information indicating whether a last
symbol of an uplink subframe for sounding reference signal (SRS)
transmissions, is available for a physical uplink shared channel
(PUSCH); and determining from the received information whether the
last symbol is available for the PUSCH, wherein the user equipment
is configured to ignore cell specific SRS subframe configuration
when determining whether the last symbol of the uplink subframe is
available for transmission of the PUSCH, wherein one bit in the
uplink grant message indicates whether the last symbol is available
for the PUSCH, and another bit in the uplink grant message
indicates whether the user equipment should send an SRS, wherein
said one bit indicating whether the last symbol is available for
the PUSCH and said one bit indicating indicate whether the user
equipment should send an SRS are interpreted jointly according to:
`00` indicates to the user equipment to not transmit an SRS, and to
puncture the PUSCH; `01` indicates to the user equipment to not
transmit an SRS, and to transmit the PUSCH in the last symbol; `10`
indicates to the user equipment to transmit an SRS, and to puncture
the PUSCH; `11` indicates to the user equipment to transmit an SRS,
and to transmit t PUSCH.
26. A method, comprising: receiving, by a user equipment, an uplink
grant message comprising information indicating whether a last
symbol of an uplink subframe for sounding reference signal (SRS)
transmissions, is available for a physical uplink shared channel
(PUSCH); and determining from the received information whether the
last symbol is available for the PUSCH, wherein the user equipment
is configured to ignore cell specific SRS subframe configuration
when determining whether the last symbol of the uplink subframe is
available for transmission of the PUSCH, wherein one bit in the
uplink grant message indicates whether the last symbol is available
for the PUSCH, and another bit in the uplink grant message
indicates whether the user equipment should send an SRS, wherein a
first and a second SRS configuration are provided, and wherein said
one bit indicating whether the last symbol is available for the
PUSCH and said one bit indicating indicate whether the UE should
send an SRS are interpreted jointly according to: `00` indicates to
not transmit an SRS, and puncture the PUSCH; `01` indicates to not
transmit an SRS, and transmit the PUSCH in the last symbol; `10`
indicates to transmit a first SRS configuration, and puncture the
PUSCH; `11` indicates to transmit a second SRS configuration, and
puncture the PUSCH.
27. The method according to claim 23, wherein the receiving further
comprises: receiving the information comprising two bits in the
uplink grant message to indicate whether the last symbol is
available for the PUSCH.
28. The method according to claim 23, wherein, when use of a new
SRS trigger type is configured, hybrid automatic repeat request
(HARQ) re-transmissions follow a pre-defined codepoint of the new
SRS trigger type or follow puncturing rules defined for an
overlapping cell-specific SRS.
29. The method according to claim 23, wherein the information
comprises a new SRS trigger type, and wherein the new SRS trigger
type has a higher priority than existing SRS trigger types.
30. An apparatus, comprising: at least one processor; and at least
one memory comprising computer program code, the at least one
memory and the computer program code, with the at least one
processor, causing the apparatus at least to receive an uplink
grant message for a physical uplink shared channel (PUSCH)
comprising information indicating whether a last symbol of an
uplink subframe that is reserved by a base station in every
n.sup.th subframe for sounding reference signal (SRS)
transmissions, is available for the PUSCH; and determine from the
received information whether the last symbol is available for the
PUSCH, wherein the apparatus is configured to ignore cell specific
SRS subframe configuration when determining whether the last symbol
of the uplink subframe is available for transmission of the
PUSCH.
31. The apparatus according to claim 30, wherein one bit in the
uplink grant message indicates whether the last symbol is available
for the PUSCH, and another bit in the uplink grant message
indicates whether the apparatus should send an SRS.
32. The apparatus according to claim 31, wherein said one bit
indicating whether the last symbol is available for the PUSCH and
said one bit indicating indicate whether the apparatus should send
an SRS are interpreted jointly according to: `00` indicates to the
apparatus to not transmit an SRS, and to puncture the PUSCH; `01`
indicates to the apparatus to not transmit an SRS, and to transmit
the PUSCH in the last symbol; `10` indicates to the apparatus to
transmit an SRS, and to puncture the PUSCH; `11` indicates to the
apparatus to transmit an SRS, and to transmit the PUSCH.
33. The apparatus according to claim 31, wherein a first and a
second SRS configuration are provided, and wherein said one bit
indicating whether the last symbol is available for the PUSCH and
said one bit indicating indicate whether the UE should send
sounding reference signal (SRS) are interpreted jointly according
to: `00` indicates to not transmit an SRS, and puncture the PUSCH;
`01` indicates to not transmit an SRS, and transmit the PUSCH in
the last symbol; `10` indicates to transmit a first SRS
configuration, and puncture the PUSCH; `11` indicates to transmit a
second SRS configuration, and puncture the PUSCH.
34. The apparatus according to claim 30, wherein the at least one
memory and the computer program code are further configured, with
the at least one processor, to cause the apparatus at least to:
receive the information comprising two bits in the uplink grant
message to indicate whether the last symbol is available for the
PUSCH.
35. The apparatus according to claim 30, wherein, when use of a new
SRS trigger type is configured, hybrid automatic repeat request
(HARQ) re-transmissions follow a pre-defined codepoint of the new
SRS trigger type or follow puncturing rules defined for an
overlapping cell-specific SRS.
36. The apparatus according to claim 30, wherein the information
comprises a new SRS trigger type, and wherein the new SRS trigger
type has a higher priority than existing SRS trigger types.
37. The apparatus according to claim 30, wherein the apparatus
comprises a user equipment.
38. A computer program, embodied on a non-transitory computer
readable medium, the computer program, when executed by a
processor, causes the processor to: receive an uplink grant message
for a physical uplink shared channel (PUSCH) comprising information
indicating whether a last symbol of an uplink subframe that is
reserved by a base station in every n.sup.th subframe for sounding
reference signal (SRS) transmissions, is available for the PUSCH;
and determine from the received information whether the last symbol
is available for the PUSCH, wherein the determining comprises
ignoring cell specific SRS subframe configuration when determining
whether the last symbol of the uplink subframe is available for
transmission of the PUSCH.
Description
BACKGROUND
1. Field
Embodiments of the invention generally relate to mobile
communications networks, such as, but not limited to, the Universal
Mobile Telecommunications System (UMTS) Terrestrial Radio Access
Network (UTRAN), Long Term Evolution (LTE) Evolved UTRAN (E-UTRAN),
and/or LTE-A.
2. Description of the Related Art
Universal Mobile Telecommunications System (UMTS) Terrestrial Radio
Access Network (UTRAN) refers to a communications network including
base stations, or Node Bs, and for example radio network
controllers (RNC). UTRAN allows for connectivity between the user
equipment (UE) and the core network. The RNC provides control
functionalities for one or more Node Bs. The RNC and its
corresponding Node Bs are called the Radio Network Subsystem (RNS).
In case of E-UTRAN (enhanced UTRAN), no RNC exists and most of the
RNC functionalities are contained in the enhanced Node B (eNodeB or
eNB).
Long Term Evolution (LTE) or E-UTRAN refers to improvements of the
UMTS through improved efficiency and services, lower costs, and use
of new spectrum opportunities. In particular, LTE is a 3GPP
standard that provides for uplink peak rates of at least 50
megabits per second (Mbps) and downlink peak rates of at least 100
Mbps. LTE supports scalable carrier bandwidths from 20 MHz down to
1.4 MHz and supports both Frequency Division Duplexing (FDD) and
Time Division Duplexing (TDD).
As mentioned above, LTE may also improve spectral efficiency in
networks, allowing carriers to provide more data and voice services
over a given bandwidth. Therefore, LTE is designed to fulfill the
needs for high-speed data and media transport in addition to
high-capacity voice support. Advantages of LTE include, for
example, high throughput, low latency, FDD and TDD support in the
same platform, an improved end-user experience, and a simple
architecture resulting in low operating costs.
Further releases of 3GPP LTE (e.g., LTE Rel-10, LTE Rel-11, LTE
Rel-12) are targeted towards future international mobile
telecommunications advanced (IMT-A) systems, referred to herein for
convenience simply as LTE-Advanced (LTE-A).
LTE-A is directed toward extending and optimizing the 3GPP LTE
radio access technologies. A goal of LTE-A is to provide
significantly enhanced services by means of higher data rates and
lower latency with reduced cost. LTE-A is a more optimized radio
system fulfilling the international telecommunication union-radio
(ITU-R) requirements for IMT-Advanced while keeping the backward
compatibility.
SUMMARY
One embodiment is directed to a method including incorporating into
an uplink grant message, by a base station in a communications
system, information on whether a last symbol of an uplink subframe
is used for physical uplink shared channel (PUSCH), for sounding
reference signal (SRS), or is empty. The method includes
transmitting the uplink grant message comprising the information on
the last symbol to a user equipment (UE).
Another embodiment is directed to an apparatus including at least
one processor and at least one memory comprising computer program
code. The at least one memory and the computer program code are
configured, with the at least one processor, to cause the apparatus
at least to incorporate, into an uplink grant message, information
on whether a last symbol of an uplink subframe is used for physical
uplink shared channel (PUSCH), for sounding reference signal (SRS),
or is empty, and to transmit the uplink grant message comprising
the information on the last symbol to a user equipment (UE).
Another embodiment is directed to a computer program, embodied on a
non-transitory computer readable medium. The computer program is
configured to control a processor to perform a process. The process
includes incorporating into an uplink grant message information on
whether a last symbol of an uplink subframe is used for physical
uplink shared channel (PUSCH), for sounding reference signal (SRS),
or is empty, and transmitting the uplink grant message comprising
the information on the last symbol to a user equipment.
An embodiment is directed to a method including receiving, by a
user equipment, an uplink grant message comprising information
indicating whether a last symbol of an uplink subframe is used for
physical uplink shared channel (PUSCH), for sounding reference
signal (SRS), or is empty. The method also includes determining
from the received information whether the last symbol is available
for physical uplink shared channel (PUSCH), or is used for sounding
reference signal (SRS) transmission, or is left empty. The user
equipment is configured to ignore cell specific SRS subframe
configuration when determining whether the last symbol of the
uplink subframe is available for transmission of PUSCH, SRS, or is
left empty.
Another embodiment is directed to an apparatus including at least
one processor and at least one memory comprising computer program
code. The at least one memory and the computer program code are
configured, with the at least one processor, to cause the apparatus
at least to receive an uplink grant message comprising information
indicating whether a last symbol of an uplink subframe is used for
physical uplink shared channel (PUSCH), for sounding reference
signal (SRS), or is empty, and to determine from the received
information whether the last symbol is available for physical
uplink shared channel (PUSCH), or is used for sounding reference
signal transmission, or is left empty. The apparatus is configured
to ignore cell specific SRS subframe configuration when determining
whether the last symbol of the uplink subframe is available for
transmission of PUSCH, SRS, or is left empty.
Another embodiment is directed to a computer program, embodied on a
non-transitory computer readable medium. The computer program is
configured to control a processor to perform a process. The process
includes receiving an uplink grant message comprising information
indicating whether a last symbol of an uplink subframe is used for
physical uplink shared channel (PUSCH), for sounding reference
signal (SRS), or is empty. The process also includes determining
from the received information whether the last symbol is available
for physical uplink shared channel (PUSCH). The determining
comprises ignoring cell specific SRS subframe configuration when
determining whether the last symbol of the uplink subframe is
available for transmission of PUSCH, SRS, or is left empty.
BRIEF DESCRIPTION OF THE DRAWINGS
For proper understanding of the invention, reference should be made
to the accompanying drawings, wherein:
FIG. 1 illustrates an example of the uplink frame structure,
according to an embodiment;
FIG. 2a illustrates an example of an apparatus, according to one
embodiment;
FIG. 2b illustrates an example of an apparatus, according to
another embodiment;
FIG. 3a illustrates a flow chart of a method, according to one
embodiment; and
FIG. 3b illustrates a flow chart of a method, according to another
embodiment.
DETAILED DESCRIPTION
It will be readily understood that the components of the invention,
as generally described and illustrated in the figures herein, may
be arranged and designed in a wide variety of different
configurations. Thus, the following detailed description of the
embodiments of systems, methods, apparatuses, and computer program
products for controlling sounding reference signal (SRS)
transmission, as represented in the attached figures, is not
intended to limit the scope of the invention, but is merely
representative of selected embodiments of the invention.
If desired, the different functions discussed below may be
performed in a different order and/or concurrently with each other.
Furthermore, if desired, one or more of the described functions may
be optional or may be combined. As such, the following description
should be considered as merely illustrative of the principles,
teachings and embodiments of this invention, and not in limitation
thereof.
The 3GPP RANI study item entitled, "Small Cell Enhancements for
E-UTRA and E-UTRAN--Physical-layer Aspects" has an objective of
identifying potential enhancements for LTE physical layer operation
in a small cell environment. The study item description mentions
that spectral efficiency improvements related to overhead reduction
of user specific reference signals should be studied. In LTE
uplink, two types of reference signals are defined: demodulation
reference signals and sounding reference signals (SRS). Embodiments
of the present invention provide an enhancement related to sounding
reference signals, for example, in a small cell environment.
Currently, in the 3GPP Release 11 specification, if the subframe is
configured as a cell specific SRS subframe, when the UE transmits
physical uplink shared channel (PUSCH), it must puncture last
single carrier frequency division multiple access (SC-FDMA) symbol
of the subframe regardless of whether the UE actually transmits SRS
or not.
As will be outlined in detail below, certain embodiments provide a
more efficient way to control SRS transmission such that more
bandwidth may become available for PUSCH transmission. More
specifically, an embodiment allows eNB control of SRS transmission
on a per UE basis rather than on a per cell basis, and enables
resources that are reserved by default for PUSCH transmission to be
used for SRS.
An LTE small cell environment can be characterized as having
following properties: UE(s) are close to the eNB, for example the
distance between the eNB and UE(s) is significantly shorter than in
a macro cell environment and, consequently, the uplink (UL) path
loss is lower than in the larger cells; UE(s) attached to a small
cell can be assumed to be low to moderate speed only (high speed
UEs are served by macro cell); number of UE(s) served by the small
cell is low; and/or number of active UE(s) may change quickly
Channel conditions can be expected to be more stable and channel
coherence bandwidth larger in a small cell when compared to a macro
cell. As a result, continuous and frequent sounding of the channel
is not needed in a small cell (UL interference characteristics can
be measured at the eNB side also without sounding signal).
FIG. 1 illustrates an example of UL frame structure in LTE Releases
8 to 11, according to one example. In the following, this may also
be referred to as a subframe. The last SC-FDMA symbol (e.g., symbol
#13) can be configured for SRS, in which case PUSCH is punctured.
Currently, as illustrated in FIG. 1, when the UE transmits PUSCH,
it must puncture the last SC-FDMA symbol (e.g., symbol #13) of the
subframe if the subframe is configured as cell specific SRS
subframe regardless of whether the UE actually transmits SRS or
not. The cell-specific configuration of SRS transmission
opportunities is periodic even with aperiodic SRS transmission,
meaning that SC-FDMA symbols are reserved deterministically in
every nth subframe, even if the need for transmitting SRS occurs
only every now and then.
Furthermore, SRS transmission bandwidth is configurable and
UE-specific SRS may occupy almost the whole UL band or just a few
physical resource blocks (PRBs). Often, especially if SRS load in
the cell is low, PUSCH transmission does not collide with
simultaneous narrow band SRS transmission, and then puncturing of
PUSCH is unnecessary.
With the Release 11 specification, the allocation of the last
subframe symbol to either PUSCH or SRS is part of cell
configuration. The SRS resources need to be dimensioned to
facilitate the highest expected number of active UEs. In a small
cell environment, such burst of UEs occurs only occasionally and
SRS load is frequently low. Then, a significant portion of resource
elements on the last symbol are not used for PUSCH or SRS.
Unnecessary puncturing of the last symbol of the PUSCH results in
loss in spectral efficiency as 1/12 of the PUSCH resources are
lost. Therefore, an efficient method to allocate last symbol of the
subframe for PUSCH or SRS would be beneficial.
When considering SRS transmission configuration for the small cell
case, an objective may be that a reduction in SRS transmissions can
be translated to more efficient PUSCH transmission. Accordingly,
certain embodiments provide that the last symbol of the subframe
can be flexibly used for PUSCH or for SRS. In one embodiment, this
may be achieved by means of a specific SRS configuration (referred
to herein as SRS configuration type B) combined with a specific SRS
trigger type (referred to herein as SRS trigger type B).
In an embodiment, a specific operation is defined for terminals
configured for SRS configuration type B. According to this
embodiment, the UE ignores cell specific SRS subframe configuration
when determining if the last symbol of the subframe is available
for transmission of PUSCH, or SRS, or is left empty. For example,
in this embodiment, the uplink grant may contain the information,
for instance in a SRS trigger type B, if the last symbol of the
subframe is used for PUSCH, for SRS, or if the symbol is left
empty. The possibility of leaving the last symbol empty can prevent
collision between PUSCH and SRS transmission from other terminals.
In other words, the possibility for dynamic muting of the last
symbol facilitates SRS transmission from other terminals on
subframes that are not contained in the cell specific SRS subframe
configuration. An example way to enable keeping the last PUSCH
SC-FDMA empty is to define zero-power SRS configuration, i.e., a
transmission similar to SRS in terms of, for example, bandwidth but
with zero power. This allows for flexible muting of the last PUSCH
symbol, making it easier to align the PUSCH/SRS transmission of
different users.
According to an embodiment, SRS configuration type B can be defined
by using existing SRS configuration and related parameters. In one
embodiment, usage of SRS trigger type B is combined with SRS
configuration type B only. The UE can support multiple parallel SRS
configuration type B, in addition to existing SRS
configurations.
Further, in an embodiment, some of the existing SRS configuration
parameters can be optimized to support improved functionality with
SRS configuration type B. For example, SRS Periodicity (TSRS) of 1
ms could be supported with SRS configuration type B (due to the
fact that SRS configuration type B does not introduce any overhead
in the case SRS is not triggered). Cell specific SRS subframe
configuration can still be used in the cell by earlier release UEs
(e.g., prior to Release 11) and UEs not configured for the new mode
provided by embodiments of the invention, such as UEs performing
initial access in the small cell. However, the density (or
periodicity) of cell specific SRS subframe configuration can be
considerably decreased (or periodicity increased) with the use of
embodiments of invention.
There can be pre-defined priorities defined between different
trigger types (i.e., trigger type 0/1 based on existing SRS
procedure and SRS trigger type B). According to an embodiment, SRS
trigger type B would have the highest priority compared to trigger
type 0 or 1. This would allow, for example, a Release 12 UE to
transmit PUSCH via resources configured for cell specific SRS
(assuming that those resources are not actually used for
transmitting SRS).
According to an embodiment, one additional bit may be included in
the uplink grant. The additional bit, e.g., "PUSCH in the last
symbol bit", can be used to inform whether the last symbol of the
subframe is available for PUSCH. When aperiodic SRS is used, one
bit in the UL grant, i.e., a "SRS request bit" informs the UE
whether it should send SRS. In one embodiment, the "SRS request
bit" and "PUSCH in the last symbol bit" may be interpreted jointly
as follows: A straightforward interpretation of the two bits may
include: `00` do not transmit SRS, puncture PUSCH; `01` do not
transmit SRS, transmit PUSCH in the last symbol; `10` transmit SRS,
puncture PUSCH; `11` transmit SRS, transmit PUSCH (transmissions
must be in non-overlapping PRBs). Simultaneous SRS and PUSCH in the
same cell may not be considered as valid option, so this
combination may be replaced by another interpretation, as discussed
below. With two different SRS configurations, an interpretation of
the two bits may include: `00` do not transmit SRS, puncture PUSCH;
`01` do not transmit SRS, transmit PUSCH in the last symbol; `10`
transmit SRS config 1, puncture PUSCH; `11` transmit SRS config 2,
puncture PUSCH.
In an embodiment, there could also be a 2-bit indication for "PUSCH
in the last symbol", for example, so that the bits are interpreted
in the following way: `00` puncture PUSCH in the last symbol; `01`
transmit part of the allocated PUSCH PRBs; `10` transmit another
part of the allocated PUSCH
PRBs; `11` transmit PUSCH.
One of the issues to solve with SRS trigger type B is the procedure
to be used with hybrid automatic repeat request (HARQ)
re-transmissions (where the trigger bits are not available).
According to an embodiment, one approach may be to have the HARQ
re-transmissions follow a pre-defined codepoint of SRS trigger type
B, e.g., `01` do not transmit SRS and transmit PUSCH in the last
symbol. Alternatively, another embodiment may follow puncturing
rules defined for overlapping cell-specific SRS (if configured). In
situations where the eNB wants to change the SRS strategy for the
retransmissions, it can use scheduled adaptive re-transmission.
FIG. 2a illustrates an example of an apparatus 10 according to an
embodiment. In one embodiment, apparatus 10 may be a base station,
such as a node B or eNB. It should be noted that one of ordinary
skill in the art would understand that apparatus 10 may include
components or features not shown in FIG. 2a. Only those components
or feature necessary for illustration of the invention are depicted
in FIG. 2a.
As illustrated in FIG. 2a, apparatus 10 includes a processor 22 for
processing information and executing instructions or operations.
Processor 22 may be any type of general or specific purpose
processor. While a single processor 22 is shown in FIG. 2a,
multiple processors may be utilized according to other embodiments.
In fact, processor 22 may include one or more of general-purpose
computers, special purpose computers, microprocessors, digital
signal processors (DSPs), field-programmable gate arrays (FPGAs),
application-specific integrated circuits (ASICs), and processors
based on a multi-core processor architecture, as examples.
Apparatus 10 further includes a memory 14, which may be coupled to
processor 22, for storing information and instructions that may be
executed by processor 22. Memory 14 may be one or more memories and
of any type suitable to the local application environment, and may
be implemented using any suitable volatile or nonvolatile data
storage technology such as a semiconductor-based memory device, a
magnetic memory device and system, an optical memory device and
system, fixed memory, and removable memory. For example, memory 14
can be comprised of any combination of random access memory (RAM),
read only memory (ROM), static storage such as a magnetic or
optical disk, or any other type of non-transitory machine or
computer readable media. The instructions stored in memory 14 may
include program instructions or computer program code that, when
executed by processor 22, enable the apparatus 10 to perform tasks
as described herein.
Apparatus 10 may also include one or more antennas 25 for
transmitting and receiving signals and/or data to and from
apparatus 10. Apparatus 10 may further include a transceiver 28
configured to transmit and receive information. For instance,
transceiver 28 may be configured to modulate information on to a
carrier waveform for transmission by the antenna(s) 25 and
demodulates information received via the antenna(s) 25 for further
processing by other elements of apparatus 10. In other embodiments,
transceiver 28 may be capable of transmitting and receiving signals
or data directly.
Processor 22 may perform functions associated with the operation of
apparatus 10 including, without limitation, precoding of antenna
gain/phase parameters, encoding and decoding of individual bits
forming a communication message, formatting of information, and
overall control of the apparatus 10, including processes related to
management of communication resources.
In an embodiment, memory 14 stores software modules that provide
functionality when executed by processor 22. The modules may
include, for example, an operating system that provides operating
system functionality for apparatus 10. The memory may also store
one or more functional modules, such as an application or program,
to provide additional functionality for apparatus 10. The
components of apparatus 10 may be implemented in hardware, or as
any suitable combination of hardware and software.
As mentioned above, according to one embodiment, apparatus 10 may
be a base station, such as a node B or eNB, for example. In an
embodiment, apparatus 10 may be controlled by memory 14 and
processor 22 to incorporate, into an uplink grant message,
information on whether a last symbol of the uplink frame structure
is used for PUSCH, is used for sounding reference signal (SRS), or
is left empty. Apparatus 10 may be controlled by memory 14 and
processor 22 to transmit the uplink grant message comprising the
information on the last symbol to a UE. In one embodiment, the
information is a new SRS trigger type (e.g., SRS trigger type B).
In one embodiment, the new SRS trigger type (e.g., SRS trigger type
B) has a higher priority than existing SRS trigger types (e.g.,
trigger type 0 or 1).
According to an embodiment, apparatus 10 may be controlled by
memory 14 and processor 22 to incorporate a single bit in the
uplink grant message to indicate whether the last symbol is
available for PUSCH, and another bit in the uplink grant message to
indicate whether the UE should send SRS. The one bit indicating
whether the last symbol is available for PUSCH and the one bit
indicating whether the UE should send sounding reference signal
(SRS) may be interpreted jointly, for example, according to the
following: `00` indicates to not transmit SRS, and puncture PUSCH;
`01` indicates to not transmit SRS, and transmit PUSCH in the last
symbol; `10` indicates to transmit SRS, and puncture PUSCH; `11`
indicates to transmit SRS, and transmit PUSCH.
In one embodiment, a first and a second SRS configuration are
provided, in which case the one bit indicating whether the last
symbol is available for PUSCH and the one bit indicating whether
the UE should send sounding reference signal (SRS) may be
interpreted jointly, for example, according to the following: `00`
indicates to not transmit SRS, and puncture PUSCH; `01` indicates
to not transmit SRS, and transmit PUSCH in the last symbol; `10`
indicates to transmit first SRS configuration, and puncture PUSCH;
`11` indicates to transmit second SRS configuration, and puncture
PUSCH.
In another embodiment, apparatus 10 may be controlled by memory 14
and processor 22 to incorporate two bits in the uplink grant
message to indicate whether the last symbol is available for
physical uplink shared channel (PUSCH). According to this
embodiment, the two bits in the uplink grant message indicating
whether the last symbol is available for physical uplink shared
channel (PUSCH) may be interpreted according to the following: `00`
indicates to puncture PUSCH in the last symbol; `01` indicates to
transmit part of the allocated PUSCH physical resource blocks
(PRBs); `10` indicates to transmit another part of the allocated
PUSCH PRBs; `11` indicates to transmit PUSCH.
According to an embodiment, apparatus 10 may be controlled by
memory 14 and processor 22 to define a zero-power sounding
reference signal (SRS) configuration to allow for flexible muting
of the last symbol. Further, in one embodiment, if the new sounding
reference signal (SRS) trigger type is used with hybrid automatic
repeat request (HARQ) re-transmissions, the hybrid automatic repeat
request (HARQ) re-transmissions can follow a pre-defined codepoint
of the new sounding reference signal (SRS) trigger type or can
follow puncturing rules defined for overlapping cell-specific
sounding reference signal (SRS) resources.
FIG. 2b illustrates an example of an apparatus 20 according to
another embodiment. In an embodiment, apparatus 20 may be a UE. It
should be noted that one of ordinary skill in the art would
understand that apparatus 20 may include components or features not
shown in FIG. 2b. Only those components or feature necessary for
illustration of the invention are depicted in FIG. 2b.
As illustrated in FIG. 2b, apparatus 20 includes a processor 32 for
processing information and executing instructions or operations.
Processor 32 may be any type of general or specific purpose
processor. While a single processor 32 is shown in FIG. 2b,
multiple processors may be utilized according to other embodiments.
In fact, processor 32 may include one or more of general-purpose
computers, special purpose computers, microprocessors, digital
signal processors (DSPs), field-programmable gate arrays (FPGAs),
application-specific integrated circuits (ASICs), and processors
based on a multi-core processor architecture, as examples.
Apparatus 20 further includes a memory 34, which may be coupled to
processor 32, for storing information and instructions that may be
executed by processor 32. Memory 34 may be one or more memories and
of any type suitable to the local application environment, and may
be implemented using any suitable volatile or nonvolatile data
storage technology such as a semiconductor-based memory device, a
magnetic memory device and system, an optical memory device and
system, fixed memory, and removable memory. For example, memory 34
can be comprised of any combination of random access memory (RAM),
read only memory (ROM), static storage such as a magnetic or
optical disk, or any other type of non-transitory machine or
computer readable media. The instructions stored in memory 34 may
include program instructions or computer program code that, when
executed by processor 32, enable the apparatus 20 to perform tasks
as described herein.
Apparatus 20 may also include one or more antennas 35 for
transmitting and receiving signals and/or data to and from
apparatus 20. Apparatus 20 may further include a transceiver 38
configured to transmit and receive information. For instance,
transceiver 38 may be configured to modulate information on to a
carrier waveform for transmission by the antenna(s) 35 and
demodulates information received via the antenna(s) 35 for further
processing by other elements of apparatus 20. In other embodiments,
transceiver 38 may be capable of transmitting and receiving signals
or data directly.
Processor 32 may perform functions associated with the operation of
apparatus 20 including, without limitation, precoding of antenna
gain/phase parameters, encoding and decoding of individual bits
forming a communication message, formatting of information, and
overall control of the apparatus 20, including processes related to
management of communication resources.
In an embodiment, memory 34 stores software modules that provide
functionality when executed by processor 32. The modules may
include, for example, an operating system that provides operating
system functionality for apparatus 20. The memory may also store
one or more functional modules, such as an application or program,
to provide additional functionality for apparatus 20. The
components of apparatus 20 may be implemented in hardware, or as
any suitable combination of hardware and software.
As mentioned above, according to one embodiment, apparatus 20 may
be a UE. In this embodiment, apparatus 20 may be controlled by
memory 34 and processor 32 to receive an uplink grant message
comprising information indicating whether a last symbol of an
uplink frame structure is used for physical uplink shared channel
(PUSCH), for sounding reference signal (SRS), or is empty.
Apparatus 20 may then be controlled by memory 34 and processor 32
to determine from the received new sounding reference signal (SRS)
trigger whether the last symbol is available for physical uplink
shared channel (PUSCH), or for sounding reference signal (SRS), or
is to be left empty.
As discussed above, the information included in the uplink grant
message may be a new SRS trigger type (e.g., SRS trigger type B)
that may have a higher priority than existing SRS trigger types
(e.g., trigger type 0 or 1). In addition, apparatus 20 may be
controlled to determine whether or not to transmit SRS or PUSCH in
the last symbol and/or whether to puncture PUSCH according to the
interpretation of bits in the uplink grant message discussed above
in connection with FIG. 2a.
FIG. 3a illustrates an example of a flow chart of a method for
controlling SRS transmission, according to one embodiment. In one
example, the method of FIG. 3a may be performed by a base station,
such as a node B or eNB. As illustrated in the example of FIG. 3a,
the method may include, at 300, incorporating, into an uplink grant
message, information on whether a last symbol of an uplink frame
structure is used for PUSCH, for SRS, or is empty. The method may
also include, at 310, transmitting the uplink grant message
comprising the information on the last symbol to a UE. In one
embodiment, the method may also include, at 320, defining a
zero-power SRS configuration.
FIG. 3b illustrates an example of a flow chart of a method for
controlling SRS transmission, according to another embodiment. In
one example, the method of FIG. 3b may be performed by a UE. As
illustrated in the example of FIG. 3b, the method may include, at
350, receiving an uplink grant message comprising information
indicating whether a last symbol of an uplink frame structure is
used for physical uplink shared channel (PUSCH), for sounding
reference signal (SRS), or is left empty. The method may then
include, at 360, determining from the received information whether
the last symbol is available for physical uplink shared channel
(PUSCH), or for sounding reference signal (SRS), or is to be left
empty.
In some embodiments, the functionality of any of the methods
described herein, such as those of FIGS. 3a and 3b, may be
implemented by software stored in memory or other computer readable
or tangible media, and executed by a processor. In other
embodiments, the functionality may be performed by hardware, for
example through the use of an application specific integrated
circuit (ASIC), a programmable gate array (PGA), a field
programmable gate array (FPGA), or any other combination of
hardware and software.
The computer readable media mentioned above may be at least
partially embodied by a transmission line, a compact disk,
digital-video disk, a magnetic disk, holographic disk or tape,
flash memory, magnetoresistive memory, integrated circuits, or any
other digital processing apparatus memory device.
Embodiments of the invention can provide several advantages. For
example, certain embodiments allow for faster triggering and
improved latency for aperiodic SRS without any increase in the SRS
overhead, as aperiodic SRS transmission does not need to "wait" for
cell-specific SRS resources. In addition, the overhead due to
resources reserved for SRS but not used can be avoided. The
implementation complexity according to certain embodiments is very
minor. Also, embodiments are fully backwards compatible in the
sense that legacy UE(s) supporting the feature do not suffer from
it at all.
The described features, advantages, and characteristics of the
invention may be combined in any suitable manner in one or more
embodiments. One skilled in the relevant art will recognize that
the invention may be practiced without one or more of the specific
features or advantages of a particular embodiment. In other
instances, additional features and advantages may be recognized in
certain embodiments that may not be present in all embodiments of
the invention.
One having ordinary skill in the art will readily understand that
the invention as discussed above may be practiced with steps in a
different order, and/or with hardware elements in configurations
which are different than those which are disclosed. Therefore,
although the invention has been described based upon these
preferred embodiments, it would be apparent to those of skill in
the art that certain modifications, variations, and alternative
constructions would be apparent, while remaining within the spirit
and scope of the invention. In order to determine the metes and
bounds of the invention, therefore, reference should be made to the
appended claims.
* * * * *