U.S. patent application number 15/268279 was filed with the patent office on 2017-08-10 for beam selection for uplink and downlink based mobility.
The applicant listed for this patent is QUALCOMM Incorporated. Invention is credited to Ravi AGARWAL, Gavin Bernard HORN, Tingfang JI, Keiichi KUBOTA, Tao LUO, John Edward SMEE, Joseph Binamira SORIAGA, Saurabha Rangrao TAVILDAR.
Application Number | 20170230869 15/268279 |
Document ID | / |
Family ID | 59498021 |
Filed Date | 2017-08-10 |
United States Patent
Application |
20170230869 |
Kind Code |
A1 |
KUBOTA; Keiichi ; et
al. |
August 10, 2017 |
BEAM SELECTION FOR UPLINK AND DOWNLINK BASED MOBILITY
Abstract
Aspects of the present disclosure provide methods and apparatus
for beam selection in uplink-based and downlink-based mobility
scenarios, for example, for new radio (NR) systems which can
improve handover reliability, reduce handover frequency, and
improve power efficiency. Certain aspects provide a method for
wireless communications by a user equipment (UE). The method
generally includes transmitting an uplink reference signal with an
indication of a preferred downlink beam and receiving a downlink
transmission based, at least in part, on the uplink reference
signal.
Inventors: |
KUBOTA; Keiichi; (San Diego,
CA) ; JI; Tingfang; (San Diego, CA) ; LUO;
Tao; (San Diego, CA) ; HORN; Gavin Bernard;
(La Jolla, CA) ; SMEE; John Edward; (San Diego,
CA) ; AGARWAL; Ravi; (San Diego, CA) ;
SORIAGA; Joseph Binamira; (San Diego, CA) ; TAVILDAR;
Saurabha Rangrao; (Jersey City, NJ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
QUALCOMM Incorporated |
San Diego |
CA |
US |
|
|
Family ID: |
59498021 |
Appl. No.: |
15/268279 |
Filed: |
September 16, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62293761 |
Feb 10, 2016 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04L 5/0048 20130101;
H04W 36/0005 20130101; Y02D 30/70 20200801; H04B 7/0639 20130101;
H04B 7/024 20130101; H04B 7/0695 20130101; H04W 48/00 20130101;
H04W 76/10 20180201 |
International
Class: |
H04W 36/00 20060101
H04W036/00; H04W 76/02 20060101 H04W076/02; H04L 5/00 20060101
H04L005/00 |
Claims
1. A method for wireless communication by a user equipment (UE),
comprising: transmitting an uplink reference signal with an
indication of a preferred downlink beam; and receiving a downlink
transmission based, at least in part, on the uplink reference
signal.
2. The method of claim 1, further comprising including an ID of the
UE in the uplink reference signal.
3. The method of claim 1, further comprising: selecting the
preferred beam during a connection establishment procedure, wherein
transmitting the uplink reference signal comprises transmitting the
uplink reference signal during the connection establishment
procedure.
4. The method of claim 3, further comprising: receiving one or more
measurement reference signals (MRSs) transmitted using different
beams; and selecting the preferred beam based on the one or more
MRSs.
5. The method of claim 4, wherein: receiving the one or more MRSs
comprises receiving the one or more MRSs from a plurality of base
stations (BSs); and selecting the preferred beam comprises the
preferred beam based on.
6. The method of claim 1, wherein: the preferred beam is selected
after a connection establishment procedure; and the uplink
reference signal is transmitted while the UE is in a connected
state.
7. The method of claim 6, further comprising: during the connection
establishment procedure, transmitting another uplink reference
signal without an indication of a preferred beam.
8. The method of claim 6, wherein: the uplink reference signal does
not include an ID of the UE.
9. The method of claim 1, further comprising: receiving a handover
command based on the uplink reference signal.
10. A method for wireless communication by a base station (BS),
comprising: receiving, from a user equipment (UE), an uplink
reference signal with an indication of a preferred downlink beam;
and transmitting a downlink transmission to the UE based, at least
in part, on the uplink reference signal.
11. The method of claim 10, wherein the uplink reference signal
includes an ID of the UE.
12. The method of claim 10, further comprising: performing a
connection establishment procedure with the UE, wherein receiving
the uplink reference signal comprises receiving the preferred beam
during the connection establishment procedure.
13. The method of claim 12, further comprising: transmitting one or
more measurement reference signals (MRSs) using different beams,
and wherein the preferred beam is based on the one or more
MRSs.
14. The method of claim 10, further comprising: performing a
connection establishment procedure with the UE, wherein receiving
the uplink reference signal comprises receiving the uplink
reference signal after the connection establishment procedure while
the UE is in a connected state.
15. The method of claim 14, further comprising: during the
connection establishment procedure, receiving another uplink
reference signal without an indication of a preferred beam.
16. The method of claim 14, wherein: the uplink reference signal
does not include an ID of the UE.
17. The method of claim 10, further comprising: transmitting a
handover command based on the uplink reference signal.
18. The method of claim 10, wherein transmitting the handover
command based on the uplink reference signal comprises transmitting
the handover command based on at least one of the indication of the
preferred beam or measurement of the uplink reference signal.
19. An apparatus for wireless communication by a user equipment
(UE), comprising: at least one processor configured to: transmit an
uplink reference signal with an indication of a preferred downlink
beam; and receive a downlink transmission based, at least in part,
on the uplink reference signal; and a memory coupled with the at
least one processor.
20. The apparatus of claim 19, wherein the at least one processor
is configured to: select the preferred beam during a connection
establishment procedure; and transmit the uplink reference signal
during the connection establishment procedure.
21. The apparatus of claim 20, wherein the at least one processor
is configured to: receive one or more measurement reference signals
(MRSs) transmitted using different beams, and select the preferred
beam based on the one or more MRSs.
22. The apparatus of claim 20, wherein the at least one processor
is configured to: select the preferred beam after a connection
establishment procedure; and transmit the uplink reference signal
while the UE is in a connected state.
23. The apparatus of claim 22, wherein the at least one processor
is further configured to: during the connection establishment
procedure, transmit another uplink reference signal without an
indication of a preferred beam.
24. The apparatus of claim 20, wherein the at least one processor
is further configured to: receive a handover command based on the
uplink reference signal.
25. An apparatus for wireless communication by a base station (BS),
comprising: at least one processor configured to: receive, from a
user equipment (UE), an uplink reference signal with an indication
of a preferred downlink beam; and transmit a downlink transmission
to the UE based, at least in part, on the uplink reference signal;
and a memory coupled with the at least one processor.
26. The apparatus of claim 25, wherein the at least one processor
is configured to: perform a connection establishment procedure with
the UE; and receive the uplink reference signal during the
connection establishment procedure.
27. The apparatus of claim 26, wherein: the at least one processor
is further configured to transmit one or more measurement reference
signals (MRSs) using different beams, and the preferred beam is
selected based on the one or more MRSs.
28. The apparatus of claim 25, wherein the at least one processor
is configured to: perform a connection establishment procedure with
the UE; and receive the uplink reference signal while the UE is in
a connected state.
29. The apparatus of claim 25, wherein the at least one processor
is configured to: transmit a handover command based on the uplink
reference signal.
30. The apparatus of claim 25, wherein the at least one processor
is configured to transmit the handover command based on at least
one of the indication of the preferred beam or measurement of the
uplink reference signal.
Description
CROSS-REFERENCE TO RELATED APPLICATION & PRIORITY CLAIM
[0001] This application claims benefit of and priority to U.S.
Provisional Patent Application Ser. No. 62/293,761, filed Feb. 10,
2016, which is herein incorporated by reference in its entirety for
all applicable purposes.
TECHNICAL FIELD
[0002] The present disclosure generally relates to wireless
communications and, more particularly, to methods and apparatus for
beam selection in uplink-based and downlink-based mobility
scenarios, for example, for new radio (NR) systems which can
improve handover reliability, reduce handover frequency, and
improve power efficiency.
INTRODUCTION
[0003] Wireless communication systems are widely deployed to
provide various telecommunication services such as telephony,
video, data, messaging, and broadcasts. Typical wireless
communication systems may employ multiple-access technologies
capable of supporting communication with multiple users by sharing
available system resources (e.g., bandwidth, transmit power).
Examples of such multiple-access technologies include code division
multiple access (CDMA) systems, time division multiple access
(TDMA) systems, frequency division multiple access (FDMA) systems,
orthogonal frequency division multiple access (OFDMA) systems,
single-carrier frequency divisional multiple access (SC-FDMA)
systems, and time division synchronous code division multiple
access (TD-SCDMA) systems.
[0004] A wireless communication network may include a number of
base stations (BS) that can support communication for a number of
user equipments (UEs). A UE may communicate with a BS via downlink
and uplink. The downlink (or forward link) refers to the
communication link from the BS to the UE, and the uplink (or
reverse link) refers to the communication link from the UE to the
BS. As will be described in more detail herein, a BS may be
referred to as a Node B, gNB, access point (AP), radio head,
transmission reception point (TRP), new radio (NR) BS, 5G Node B,
etc.).
[0005] These multiple access technologies have been adopted in
various telecommunication standards to provide a common protocol
that enables different wireless devices to communicate on a
municipal, national, regional, and even global level. An example of
an emerging telecommunication standard is new radio (NR), for
example, 5G radio access. NR is a set of enhancements to the LTE
mobile standard promulgated by Third Generation Partnership Project
(3GPP). It is designed to better support mobile broadband Internet
access by improving spectral efficiency, lowering costs, improving
services, making use of new spectrum, and better integrating with
other open standards using OFDMA with a cyclic prefix (CP) on the
downlink (DL) and on the uplink (UL) as well as support
beamforming, multiple-input multiple-output (MIMO) antenna
technology, and carrier aggregation. However, as the demand for
mobile broadband access continues to increase, there exists a need
for further improvements in NR technology. Preferably, these
improvements should be applicable to other multi-access
technologies and the telecommunication standards that employ these
technologies.
[0006] Some wireless communication standards base user equipment
handoff decisions based, at least in part, on downlink
measurements. Future generation wireless communication may focus on
user-centric networks. Accordingly, apparatus, methods, processing
systems, and computer program products for new radio (NR) (new
radio access technology or 5G technology) are desirable.
BRIEF SUMMARY
[0007] The systems, methods, and devices of the disclosure each
have several aspects, no single one of which is solely responsible
for its desirable attributes. Without limiting the scope of this
disclosure as expressed by the claims which follow, some features
will now be discussed briefly. After considering this discussion,
and particularly after reading the section entitled "Detailed
Description" one will understand how the features of this
disclosure provide advantages that include improved communications
between access points and stations in a wireless network.
[0008] Certain aspects of the present disclosure generally relate
to methods and apparatus for beam selection in uplink-based and
downlink-based mobility scenarios. For example, a downlink beam
used for downlink signaling and/or a handover command (and selected
transmission point) by a base station (BS) can be based on
measurement of an uplink reference signal from the user equipment
(UE) and/or based on an indication in the uplink reference signal
of a preferred beam and/or transmission point.
[0009] Certain aspects of the present disclosure provide a method
for wireless communication by a UE. The method generally includes
transmitting an uplink reference signal with an indication of a
preferred downlink beam and receiving a downlink transmission
based, at least in part, on the uplink reference signal.
[0010] Certain aspects of the present disclosure provide an
apparatus for wireless communication by a UE. The apparatus
generally includes means for transmitting an uplink reference
signal with an indication of a preferred downlink beam and means
for receiving a downlink transmission based, at least in part, on
the uplink reference signal.
[0011] Certain aspects of the present disclosure provide an
apparatus for wireless communication by a UE. The apparatus
generally includes at least one processor and a memory coupled with
the at least one processor. The at least one processor is generally
configured to transmit an uplink reference signal with an
indication of a preferred downlink beam and receive a downlink
transmission based, at least in part, on the uplink reference
signal.
[0012] Certain aspects of the present disclosure provide a computer
readable medium storing computer executable code for causing a UE
to transmit an uplink reference signal with an indication of a
preferred downlink beam and receive a downlink transmission based,
at least in part, on the uplink reference signal.
[0013] Certain aspects of the present disclosure provide a method
for wireless communication by a BS. The method generally includes
receiving, from a UE, an uplink reference signal with an indication
of a preferred downlink beam and transmitting a downlink
transmission to the UE based, at least in part, on the uplink
reference signal.
[0014] Certain aspects of the present disclosure provide an
apparatus for wireless communication by a BS. The apparatus
generally includes means for receiving, from a UE, an uplink
reference signal with an indication of a preferred downlink beam
and means for transmitting a downlink transmission to the UE based,
at least in part, on the uplink reference signal.
[0015] Certain aspects of the present disclosure provide an
apparatus for wireless communication by a BS. The apparatus
generally includes at least one processor and a memory coupled with
the at least one processor. The at least one processor is generally
configured to receive, from a UE, an uplink reference signal with
an indication of a preferred downlink beam and transmit a downlink
transmission to the UE based, at least in part, on the uplink
reference signal.
[0016] Certain aspects of the present disclosure provide a computer
readable medium storing computer executable code for causing a BS
to receive, from a UE, an uplink reference signal with an
indication of a preferred downlink beam and transmit a downlink
transmission to the UE based, at least in part, on the uplink
reference signal.
[0017] Aspects generally include methods, apparatus, systems,
computer program products, and processing systems, as substantially
described herein with reference to and as illustrated by the
accompanying drawings.
[0018] Other aspects, features, and embodiments of the present
invention will become apparent to those of ordinary skill in the
art, upon reviewing the following description of specific,
exemplary embodiments of the present invention in conjunction with
the accompanying figures. While features of the present invention
may be discussed relative to certain embodiments and figures below,
all embodiments of the present invention can include one or more of
the advantageous features discussed herein. In other words, while
one or more embodiments may be discussed as having certain
advantageous features, one or more of such features may also be
used in accordance with the various embodiments of the invention
discussed herein. In similar fashion, while exemplary embodiments
may be discussed below as device, system, or method embodiments it
should be understood that such exemplary embodiments can be
implemented in various devices, systems, and methods.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] So that the manner in which the above-recited features of
the present disclosure can be understood in detail, a more
particular description, briefly summarized above, may be had by
reference to aspects, some of which are illustrated in the appended
drawings. The appended drawings illustrate only certain typical
aspects of this disclosure, however, and are therefore not to be
considered limiting of its scope, for the description may admit to
other equally effective aspects.
[0020] FIG. 1 illustrates an exemplary deployment in which multiple
wireless networks have overlapping coverage, in accordance with
certain aspects of the disclosure.
[0021] FIG. 2 is a diagram illustrating an example of an access
network, in accordance with certain aspects of the disclosure.
[0022] FIG. 3 is a diagram illustrating an example of a DL frame
structure in a telecommunications system, in accordance with
certain aspects of the disclosure.
[0023] FIG. 4 is a diagram illustrating an example of an UL frame
structure in a telecommunications system, in accordance with
certain aspects of the disclosure.
[0024] FIG. 5 is a diagram illustrating an example of radio
protocol architecture for the user and control plane, in accordance
with certain aspects of the disclosure.
[0025] FIG. 6 is a diagram illustrating an example of a base
station (BS) and user equipment (UE) in an access network, in
accordance with certain aspects of the disclosure.
[0026] FIG. 7 illustrates an example logical architecture of a
distributed radio access network (RAN), in accordance with certain
aspects of the present disclosure.
[0027] FIG. 8 illustrates an example physical architecture of a
distributed RAN, in accordance with certain aspects of the present
disclosure.
[0028] FIG. 9 is a diagram illustrating an example of a downlink
(DL)-centric subframe, in accordance with certain aspects of the
present disclosure.
[0029] FIG. 10 is a diagram illustrating an example of an uplink
(UL)-centric subframe, in accordance with certain aspects of the
present disclosure.
[0030] FIG. 11 is a call-flow diagram illustrating an example
downlink-based handover procedure, in accordance with certain
aspects of the disclosure.
[0031] FIG. 12 is a call-flow diagram illustrating an example
uplink-based handover procedure, in accordance with certain aspects
of the disclosure.
[0032] FIG. 13 is a call flow illustrating example operations,
performed by a UE, for uplink-based mobility, in accordance with
certain aspects of the disclosure.
[0033] FIG. 14 is a call flow illustrating example operations,
performed by a source or target BS, for uplink-based mobility, in
accordance with certain aspects of the disclosure.
[0034] FIG. 15 illustrates an example state diagram showing example
UE-centric uplink-based mobility, in accordance with certain
aspects of the disclosure.
[0035] FIG. 16 is call flow diagram illustrating beam selection for
uplink-based mobility, in accordance with aspects of the present
disclosure.
[0036] FIG. 17 illustrates example operations, performed by a UE,
for beam selection for downlink-mobility, in accordance with
certain aspects of the disclosure.
[0037] FIG. 18 illustrates example operations, performed by a BS,
for beam selection for downlink-based mobility, in accordance with
certain aspects of the disclosure.
[0038] FIG. 19 illustrates an example call flow diagram for beam
selection, during an initial access procedure, for downlink-based
mobility, in accordance with certain aspects of the disclosure.
[0039] FIG. 20 illustrates an example call flow diagram for beam
selection, after an initial access procedure, for downlink-based
mobility, in accordance with certain aspects of the disclosure.
[0040] To facilitate understanding, identical reference numerals
have been used, where possible, to designate identical elements
that are common to the figures. It is contemplated that elements
disclosed in one aspect may be beneficially utilized on other
aspects without specific recitation.
DETAILED DESCRIPTION
[0041] Aspects of the present disclosure provide apparatus,
methods, processing systems, and computer program products for new
radio (NR) (new radio access technology or 5G technology).
[0042] Aspects of the present disclosure provide techniques and
apparatus for performing a straight-forward, quick, and
resource-efficient handover procedure. As described herein, for
uplink-based mobility, handovers may be performed based, at least
in part, on uplink signal measurements taken by base stations
(e.g., Node Bs (NBs), gNBs, access points (APs), smart radio heads
(SRHs), transmission reception points (TRPs), NR BSs, 5G NBs,
etc.), while for downlink-based mobility, handovers may be
performed based on measurements taken by UEs. For example, 5G and
other future communications systems may focus on creating a more
user-centric network.
[0043] Aspects of the present disclosure provide a framework for
(forward and backward) handover based on uplink and/or downlink
measurements. In addition, 5G and other telecommunications may use
beamformed transmissions. Aspects of the present disclosure also
provide for beam selection techniques for both uplink-based and
downlink-based mobility scenarios.
[0044] In downlink-based mobility, a UE may receive reference
signals (e.g., measurement reference signals (MRS) from a BS and
report measurements to the BS. The UE can also report a preferred
beam and/or a preferred transmission point. The indication of the
preferred beam and/or transmission point may be included in an
uplink reference signal from the UE. Mobility decisions (e.g., for
a handover command) at the BS can be based on measurement of the
uplink reference signal and/or based on the indication in the
uplink reference signal of the preferred beam and/or transmission
point. The BS can also use the indication of the preferred beam for
beamforming downlink signals to the UE.
[0045] In uplink-based mobility, a BS may make mobility decisions
based on measurements of an uplink reference signal from a UE
(e.g., without sending any MRS). The BS can also make the beam
selection and/or transmission point selection.
[0046] In a hybrid mobility scheme, a BS can make mobility
decisions and beam selection decisions based on reference signal
parameters, for example, similar to the uplink-based mobility. In
addition, the BS can also transmit MRSs and can refine the mobility
decision and/or beam selection based on feedback from a UE (e.g.,
in the uplink reference signals).
[0047] Advantageously, a UE may receive a configuration for an
uplink reference signal from a serving BS. A non-serving BS (e.g.,
a target BS) may receive a configuration for the uplink reference
signal from the serving BS. In this manner, the UE may transmit the
uplink reference signal which the target BS may receive. As
described herein, either the source or target BS may transmit a
handover command and/or connection reconfiguration message based,
at least in part, on measurements of the received uplink reference
signal.
[0048] Various aspects of the disclosure are described more fully
hereinafter with reference to the accompanying drawings. This
disclosure may, however, be embodied in many different forms and
should not be construed as limited to any specific structure or
function presented throughout this disclosure. Rather, these
aspects are provided so that this disclosure will be thorough and
complete, and will fully convey the scope of the disclosure to
those skilled in the art. Based on the teachings herein one skilled
in the art should appreciate that the scope of the disclosure is
intended to cover any aspect of the disclosure disclosed herein,
whether implemented independently of or combined with any other
aspect of the disclosure. For example, an apparatus may be
implemented or a method may be practiced using any number of the
aspects set forth herein. In addition, the scope of the disclosure
is intended to cover such an apparatus or method which is practiced
using other structure, functionality, or structure and
functionality in addition to or other than the various aspects of
the disclosure set forth herein. It should be understood that any
aspect of the disclosure disclosed herein may be embodied by one or
more elements of a claim.
[0049] The word "exemplary" is used herein to mean "serving as an
example, instance, or illustration." Any aspect described herein as
"exemplary" is not necessarily to be construed as preferred or
advantageous over other aspects. Yes in some scenarios, the example
can be preferred.
[0050] Although particular aspects are described herein, many
variations and permutations of these aspects fall within the scope
of the disclosure. Although some benefits and advantages of the
preferred aspects are mentioned, the scope of the disclosure is not
intended to be limited to particular benefits, uses, or objectives.
Rather, aspects of the disclosure are intended to be broadly
applicable to different wireless technologies, system
configurations, networks, and transmission protocols, some of which
are illustrated by way of example in the figures and in the
following description of the preferred aspects. The detailed
description and drawings are merely illustrative of the disclosure
rather than limiting, the scope of the disclosure being defined by
the appended claims and equivalents thereof.
[0051] The detailed description set forth below in connection with
the appended drawings is intended as a description of various
configurations and is not intended to represent the only
configurations in which the concepts described herein may be
practiced. The detailed description includes specific details for
the purpose of providing a thorough understanding of various
concepts. However, it will be apparent to those skilled in the art
that these concepts may be practiced without these specific
details. In some instances, well-known structures and components
are shown in block diagram form in order to avoid obscuring such
concepts.
[0052] Several aspects of telecommunication systems will now be
presented with reference to various apparatus and methods. These
apparatus and methods will be described in the following detailed
description and illustrated in the accompanying drawings by various
blocks, modules, components, circuits, steps, processes,
algorithms, etc. (collectively referred to as "elements"). These
elements may be implemented using hardware, software/firmware, or
combinations thereof. Whether such elements are implemented as
hardware or software depends upon the particular application and
design constraints imposed on the overall system.
[0053] By way of example, an element, or any portion of an element,
or any combination of elements may be implemented with a
"processing system" that includes one or more processors. Examples
of processors include microprocessors, microcontrollers, digital
signal processors (DSPs), field programmable gate arrays (FPGAs),
programmable logic devices (PLDs), state machines, gated logic,
discrete hardware circuits, and other suitable hardware configured
to perform the various functionality described throughout this
disclosure. One non-limiting example of the processors is the
Snapdragon processor. One or more processors in the processing
system may execute software. Software shall be construed broadly to
mean instructions, instruction sets, code, code segments, program
code, programs, subprograms, software modules, applications,
software applications, software packages, routines, subroutines,
objects, executables, threads of execution, procedures, functions,
etc., whether referred to as software/firmware, middleware,
microcode, hardware description language, or otherwise.
[0054] Accordingly, in one or more exemplary embodiments, the
functions described may be implemented in hardware,
software/firmware, or combinations thereof. If implemented in
software, the functions may be stored or transmitted over as one or
more instructions or code on a computer-readable medium. Software
shall be construed broadly to mean instructions, data, or any
combination thereof, whether referred to as software, firmware,
middleware, microcode, hardware description language, or otherwise.
Computer-readable media include both computer storage media and
communication media including any medium that facilitates transfer
of a computer program from one place to another. The processor may
be responsible for managing the bus and general processing,
including the execution of software modules stored on the
machine-readable storage media.
[0055] A computer-readable storage medium may be coupled to a
processor such that the processor can read information from, and
write information to, the storage medium. In the alternative, the
storage medium may be integral to the processor. By way of example,
the machine-readable media may include a transmission line, a
carrier wave modulated by data, and/or a computer readable storage
medium with instructions stored thereon separate from the wireless
node, all of which may be accessed by the processor through the bus
interface. Alternatively, or in addition, the machine-readable
media, or any portion thereof, may be integrated into the
processor, such as the case may be with cache and/or general
register files. Examples of machine-readable storage media may
include, by way of example, RAM (Random Access Memory), flash
memory, ROM (Read Only Memory), PROM (Programmable Read-Only
Memory), EPROM (Erasable Programmable Read-Only Memory), EEPROM
(Electrically Erasable Programmable Read-Only Memory), registers,
magnetic disks, optical disks, hard drives, or any other suitable
storage medium, or any combination thereof. The machine-readable
media may be embodied in a computer-program product.
[0056] A software module may comprise a single instruction, or many
instructions, and may be distributed over several different code
segments, among different programs, and across multiple storage
media. The computer-readable media may comprise a number of
software modules. The software modules include instructions that,
when executed by an apparatus such as a processor, cause the
processing system to perform various functions. The software
modules may include a transmission module and a receiving module.
Each software module may reside in a single storage device or be
distributed across multiple storage devices. By way of example, a
software module may be loaded into RAM from a hard drive when a
triggering event occurs. During execution of the software module,
the processor may load some of the instructions into cache to
increase access speed. One or more cache lines may then be loaded
into a general register file for execution by the processor. When
referring to the functionality of a software module below, it will
be understood that such functionality is implemented by the
processor when executing instructions from that software
module.
[0057] Also, any connection is properly termed a computer-readable
medium. For example, if the software is transmitted from a website,
server, or other remote source using a coaxial cable, fiber optic
cable, twisted pair, digital subscriber line (DSL), or wireless
technologies such as infrared (IR), radio, and microwave, then the
coaxial cable, fiber optic cable, twisted pair, DSL, or wireless
technologies such as infrared, radio, and microwave are included in
the definition of medium. Disk and disc, as used herein, include
compact disc (CD), laser disc, optical disc, digital versatile disc
(DVD), floppy disk, and Blu-ray.RTM. disc where disks usually
reproduce data magnetically, while discs reproduce data optically
with lasers. Thus, in some aspects computer-readable media may
comprise non-transitory computer-readable media (e.g., tangible
media). In addition, for other aspects computer-readable media may
comprise transitory computer-readable media (e.g., a signal).
Combinations of the above should also be included within the scope
of computer-readable media.
[0058] Thus, certain aspects may comprise a computer program
product and/or computer readable medium for performing the
operations presented herein. For example, such a computer program
product may comprise a computer-readable medium having instructions
stored (and/or encoded) thereon, the instructions being executable
by one or more processors to perform the operations described
herein.
[0059] Further, it should be appreciated that modules and/or other
appropriate means for performing the methods and techniques
described herein can be downloaded and/or otherwise obtained by a
user terminal and/or base station as applicable. For example, such
a device can be coupled to a server to facilitate the transfer of
means for performing the methods described herein. Alternatively,
various methods described herein can be provided via storage means
(e.g., RAM, ROM, a physical storage medium such as a compact disc
(CD) or floppy disk, etc.), such that a user terminal and/or base
station can obtain the various methods upon coupling or providing
the storage means to the device. Moreover, any other suitable
technique for providing the methods and techniques described herein
to a device can be utilized.
[0060] The techniques described herein may be used for various
wireless communication networks such as code division multiple
access (CDMA), time division multiple access (TDMA), frequency
division multiple access (FDMA), orthogonal FDMA (OFDMA), single
carrier FDMA (SC-FDMA) and other networks. The terms "network" and
"system"" are often used interchangeably. A CDMA network may
implement a radio access technology (RAT) such as universal
terrestrial radio access (UTRA), cdma2000, etc. UTRA includes
wideband CDMA (WCDMA) and other variants of CDMA. cdma2000 covers
IS-2000, IS-95 and IS-856 standards. IS-2000 is also referred to as
1.times. radio transmission technology (1.times.RTT), CDMA2000
1.times., etc. A TDMA network may implement a RAT such as global
system for mobile communications (GSM), enhanced data rates for GSM
evolution (EDGE), or GSM/EDGE radio access network (GERAN). An
OFDMA network may implement a RAT such as evolved UTRA (E-UTRA),
ultra mobile broadband (UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16
(WiMAX), IEEE 802.20, Flash-OFDM.RTM., etc. UTRA and E-UTRA are
part of universal mobile telecommunication system (UMTS). 3GPP
long-term evolution (LTE) and LTE-Advanced (LTE-A) are releases of
UMTS that use E-UTRA, which employs OFDMA on the downlink and
SC-FDMA on the uplink. UTRA, E-UTRA, UMTS, LTE, LTE-A and GSM are
described in documents from an organization named "3rd Generation
Partnership Project" (3GPP). cdma2000 and UMB are described in
documents from an organization named "3rd Generation Partnership
Project 2" (3GPP2). The techniques described herein may be used for
the wireless networks and RATs mentioned above as well as other
wireless networks and RATs.
[0061] It is noted that while aspects may be described herein using
terminology commonly associated with 3G and/or 4G wireless
technologies, aspects of the present disclosure can be applied in
other generation-based communication systems, such as 5G and later,
including NR technologies.
An Example Wireless Communication System
[0062] FIG. 1 illustrates an example deployment in which aspects of
the present disclosure may be implemented. For example, a user
equipment (UE) 110 transmits an uplink reference signal to a base
station (BS) 122 (e.g., a gNB, a transmission reception point
(TRP), Node B (NB), 5G NB, access point (AP), new radio (NR) BS,
etc.). The uplink reference signal can include an indication of a
preferred downlink beam. The UE 110 can receive a downlink from the
BS 122 based, at least in part, on the uplink reference signal. For
downlink-based mobility, the UE 110 may receive measurement
reference signals (MRS) transmitted with different beams from the
BS 122. The UE 110 can select the preferred beam based on the MRS.
The BS 122 can beamform the downlink signal to the UE using the
preferred beam and/or the BS 122 can send a handover command to the
UE 110 based, at least in part, on the uplink reference signal. For
uplink-based mobility the UE 110 sends the uplink reference signal,
without MRS from the BS 122, and the BS 122 can perform beam
selection and/or handover decisions based on measurement of the
uplink reference signal. In some cases a non-serving BS can receive
the uplink reference signals and send a handover command to the UE
110.
[0063] FIG. 1 shows an exemplary deployment in which multiple
wireless networks have overlapping coverage. The system illustrated
in FIG. 1 may include, for example, an evolved universal
terrestrial radio access network (E-UTRAN) 120 may support long
term evolution (LTE) and a GMS network 130. According to aspects,
the system illustrated in FIG. 1 may include one or more other
networks, such as a NR network. The radio access network may
include a number of s 122 BSs and other network entities that can
support wireless communication for UEs. In some cases, a NR network
may include a central unit (CU) and distributed units (DUs).
[0064] Each BS may provide communication coverage for a particular
geographic area. The term "cell" can refer to a coverage area of a
BS or BS subsystem serving this coverage area. A serving gateway
(S-GW) 124 may communicate with E-UTRAN 120 and may perform various
functions such as packet routing and forwarding, mobility
anchoring, packet buffering, initiation of network-triggered
services, etc. A mobility management entity (MME) 126 may
communicate with E-UTRAN 120 and serving gateway 124 and may
perform various functions such as mobility management, bearer
management, distribution of paging messages, security control,
authentication, gateway selection, etc. The network entities in LTE
are described in 3GPP TS 36.300, entitled "Evolved Universal
Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial
Radio Access Network (E-UTRAN); Overall description," which is
publicly available.
[0065] In NR systems, the term "cell" and gNB, Node B, 5G NB, or
TRP may be interchangeable. In some examples, a cell may not
necessarily be stationary, and the geographic area of the cell may
move according to the location of a mobile base station. In some
examples, the base stations may be interconnected to one another
and/or to one or more other base stations or network nodes (not
shown) in the access network 100 through various types of backhaul
interfaces such as a direct physical connection, a virtual network,
or the like using any suitable transport network.
[0066] A radio access network (RAN) 130 may support GSM and may
include a number of base stations 132 and other network entities
that can support wireless communication for UEs. A mobile switching
center (MSC) 134 may communicate with the RAN 130 and may support
voice services, provide routing for circuit-switched calls, and
perform mobility management for UEs located within the area served
by MSC 134. Optionally, an inter-working function (IWF) 140 may
facilitate communication between MME 126 and MSC 134 (e.g., for
1.times.CSFB).
[0067] E-UTRAN 120, serving gateway 124, and MME 126 may be part of
an LTE network 102. RAN 130 and MSC 134 may be part of a GSM
network 104. For simplicity, FIG. 1 shows only some network
entities in the LTE network 102 and the GSM network 104. The LTE
and GSM networks may also include other network entities that may
support various functions and services.
[0068] In general, any number of wireless networks may be deployed
in a given geographic area. Each wireless network may support a
particular RAT and may operate on one or more frequencies. A RAT
may also be referred to as a radio technology, an air interface,
etc. A frequency may also be referred to as a carrier, a frequency
channel, etc. Each frequency may support a single RAT in a given
geographic area in order to avoid interference between wireless
networks of different RATs. In some cases, NR or 5G RAT networks
may be deployed.
[0069] A UE 110 may be stationary or mobile and may also be
referred to as a mobile station, a terminal, an access terminal, a
subscriber unit, a station, etc. A UE may also be referred to as an
access terminal, a terminal, a mobile station, a subscriber unit, a
station, etc. A UE may be a Customer Premises Equipment (CPE), a
cellular phone (e.g., a smart phone), a personal digital assistant
(PDA), a wireless modem, a wireless communication device, a
handheld device, a laptop computer, a cordless phone, a wireless
local loop (WLL) station, a tablet, a camera, a gaming device, a
netbook, a smartbook, an ultrabook, medical device or equipment,
biometric sensors/devices, mammal implant device, wearable devices
(smart watches, smart clothing, smart glasses, smart wrist bands,
smart jewelry (e.g., smart ring, smart bracelet)), an entertainment
device (e.g., a music or video device, or a satellite radio), a
vehicular component or sensor, smart meters/sensors, industrial
manufacturing equipment, military firearm or communication device,
a global positioning system device, or any other suitable device
that is configured to communicate via a wireless or wired medium.
Some UEs may be considered evolved or enhanced machine-type
communication (eMTC) UEs. MTC and eMTC UEs include, for example,
robots, drones, remote devices, such as sensors, meters, monitors,
location tags, etc., that may communicate with a base station,
another device (e.g., remote device), or some other entity. A
wireless node may provide, for example, connectivity for or to a
network (e.g., a wide area network such as Internet or a cellular
network) via a wired or wireless communication link. Some UEs may
be considered Internet-of-Things (IoT) devices.
[0070] Upon power up, UE 110 may search for wireless networks from
which it can receive communication services. If more than one
wireless network is detected, then a wireless network with the
highest priority may be selected to serve UE 110 and may be
referred to as the serving network. UE 110 may perform registration
with the serving network, if necessary. UE 110 may then operate in
a connected mode to actively communicate with the serving network.
Alternatively, UE 110 may operate in an idle mode and camp on the
serving network if active communication is not required by UE
110.
[0071] UE 110 may be located within the coverage of cells of
multiple frequencies and/or multiple RATs while in the idle mode.
For LTE, UE 110 may select a frequency and a RAT to camp on based
on a priority list. This priority list may include a set of
frequencies, a RAT associated with each frequency, and a priority
of each frequency. For example, the priority list may include three
frequencies X, Y and Z. Frequency X may be used for LTE and may
have the highest priority, frequency Y may be used for GSM and may
have the lowest priority, and frequency Z may also be used for GSM
and may have medium priority. In general, the priority list may
include any number of frequencies for any set of RATs and may be
specific for the UE location. UE 110 may be configured to prefer
LTE, when available, by defining the priority list with LTE
frequencies at the highest priority and with frequencies for other
RATs at lower priorities, e.g., as given by the example above.
[0072] UE 110 may operate in the idle mode as follows. UE 110 may
identify all frequencies/RATs on which it is able to find a
"suitable" cell in a normal scenario or an "acceptable" cell in an
emergency scenario, where "suitable" and "acceptable" are specified
a standard (e.g., LTE). UE 110 may then camp on the frequency/RAT
with the highest priority among all identified frequencies/RATs. UE
110 may remain camped on this frequency/RAT until either (i) the
frequency/RAT is no longer available at a predetermined threshold
or (ii) another frequency/RAT with a higher priority reaches this
threshold. This operating behavior for UE 110 in the idle mode is
described in 3GPP TS 36.304, entitled "Evolved Universal
Terrestrial Radio Access (E-UTRA); User Equipment (UE) procedures
in idle mode," which is publicly available.
[0073] UE 110 may be able to receive packet-switched (PS) data
services from LTE network 102 and may camp on the LTE network while
in the idle mode. LTE network 102 may have limited or no support
for voice-over-Internet protocol (VoIP), which may often be the
case for early deployments of LTE networks. Due to the limited VoIP
support, UE 110 may be transferred to another wireless network of
another RAT for voice calls. This transfer may be referred to as
circuit-switched (CS) fallback. UE 110 may be transferred to a RAT
that can support voice service such as 1.times.RTT, WCDMA, GSM,
etc. For call origination with CS fallback, UE 110 may initially
become connected to a wireless network of a source RAT (e.g., LTE)
that may not support voice service. The UE may originate a voice
call with this wireless network and may be transferred through
higher-layer signaling to another wireless network of a target RAT
that can support the voice call. The higher-layer signaling to
transfer the UE to the target RAT may be for various procedures,
e.g., connection release with redirection, PS handover, etc.
[0074] In some examples, access to the air interface may be
scheduled. A scheduling entity (e.g., a base station) can allocate
resources for communication among some or all devices and equipment
within its service area or cell. Within the present disclosure, as
discussed further below, the scheduling entity may be responsible
for scheduling, assigning, reconfiguring, and releasing resources
for one or more subordinate entities. That is, for scheduled
communication, subordinate entities utilize resources allocated by
the scheduling entity.
[0075] Base stations are not the only entities that may function as
a scheduling entity. That is, in some examples, a UE may function
as a scheduling entity, scheduling resources for one or more
subordinate entities (e.g., one or more other UEs). In this
example, the UE is functioning as a scheduling entity, and other
UEs utilize resources scheduled by the UE for wireless
communication. A UE may function as a scheduling entity in a
peer-to-peer (P2P) network, and/or in a mesh network. In a mesh
network example, UEs may optionally communicate directly with one
another in addition to communicating with the scheduling
entity.
[0076] Thus, in a wireless communication network with a scheduled
access to time-frequency resources and having a cellular
configuration, a P2P configuration, and a mesh configuration, a
scheduling entity and one or more subordinate entities may
communicate utilizing the scheduled resources.
[0077] FIG. 2 is a diagram illustrating an example of an access
network 200. UE 206 may transmit an uplink reference signal which
may be received by both a serving and non-serving BSs 204, 208.
Serving and non-serving BSs 204, 208 may receive the uplink
reference signal and either of the BSs may transmit a handover
command to the UE based, at least in part, on the uplink reference
signal. The uplink reference signal can include an indication of a
preferred downlink beam. For downlink-based mobility, the UE 206
may receive measurement reference signals (MRS) transmitted with
different beams from the BS 204. The UE 206 can select the
preferred beam based on the MRS. The BS 204 can beamform the
downlink signal to the UE using the preferred beam and/or the BS
204 can send a handover command to the UE 206 based, at least in
part, on the uplink reference signal. For uplink-based mobility the
UE 206 sends the uplink reference signal, without MRS from the BS
204, and the BS 204 can perform beam selection and/or handover
decisions based on measurement of the uplink reference signal. In
some cases a non-serving BS 208 can receive the uplink reference
signals and send a handover command to the UE 206.
[0078] In FIG. 2, the access network 200 is divided into a number
of cellular regions (cells) 202. One or more lower power class BS
208 may have cellular regions 210 that overlap with one or more of
the cells 202. A lower power class BS 208 may be referred to as a
remote radio head (RRH). The lower power class BS 208 may be a
femto cell (e.g., home NB (HNB)), pico cell, or micro cell. The
macro NBs 204 are each assigned to a respective cell 202 and are
configured to provide an access point to the EPC 110 for all the
UEs 206 in the cells 202. There is no centralized controller in
this example of an access network 200, but a centralized controller
may be used in alternative configurations. The BSs 204 are
responsible for all radio related functions including radio bearer
control, admission control, mobility control, scheduling, security,
and connectivity to the serving gateway 124.
[0079] The modulation and multiple access scheme employed by the
access network 200 may vary depending on the particular
telecommunications standard being deployed. In LTE applications,
OFDM is used on the DL and SC-FDMA is used on the UL to support
both frequency division duplexing (FDD) and time division duplexing
(TDD). As those skilled in the art will readily appreciate from the
detailed description to follow, the various concepts presented
herein are well suited for LTE applications. However, these
concepts may be readily extended to other telecommunication
standards employing other modulation and multiple access
techniques. By way of example, these concepts may be extended to
Evolution-Data Optimized (EV-DO) or Ultra Mobile Broadband (UMB).
EV-DO and UMB are air interface standards promulgated by the 3rd
Generation Partnership Project 2 (3GPP2) as part of the CDMA2000
family of standards and employs CDMA to provide broadband Internet
access to mobile stations. These concepts may also be extended to
Universal Terrestrial Radio Access (UTRA) employing Wideband-CDMA
(W-CDMA) and other variants of CDMA, such as TD-SCDMA; Global
System for Mobile Communications (GSM) employing TDMA; and Evolved
UTRA (E-UTRA), Ultra Mobile Broadband (UMB), IEEE 802.11 (Wi-Fi),
IEEE 802.16 (WiMAX), IEEE 802.20, and Flash-OFDM employing OFDMA.
UTRA, E-UTRA, UMTS, LTE and GSM are described in documents from the
3GPP organization. CDMA2000 and UMB are described in documents from
the 3GPP2 organization. The actual wireless communication standard
and the multiple access technology employed will depend on the
specific application, the overall design constraints imposed on the
system, or desired operating parameters.
[0080] The BS 204 may have multiple antennas supporting MIMO
technology (e.g., massive MIMO). The use of MIMO technology enables
the BS 204 to exploit the spatial domain to support spatial
multiplexing, beamforming, and transmit diversity. Spatial
multiplexing may be used to transmit different streams of data
simultaneously on the same frequency. The data streams may be
transmitted to a single UE 206 to increase the data rate or to
multiple UEs 206 to increase the overall system capacity. This is
achieved by spatially precoding each data stream (e.g., applying a
scaling of an amplitude and a phase) and then transmitting each
spatially precoded stream through multiple transmit antennas on the
DL. The spatially precoded data streams arrive at the UE(s) 206
with different spatial signatures, which enables each of the UE(s)
206 to recover the one or more data streams destined for that UE
206. On the UL, each UE 206 transmits a spatially precoded data
stream, which enables the BS 204 to identify the source of each
spatially precoded data stream.
[0081] Spatial multiplexing is generally used when channel
conditions are good. When channel conditions are less favorable,
beamforming may be used to focus the transmission energy in one or
more directions. This may be achieved by spatially precoding the
data for transmission through multiple antennas. To achieve good
coverage at the edges of the cell, a single stream beamforming
transmission may be used in combination with transmit
diversity.
[0082] In the detailed description that follows, various aspects of
an access network will be described with reference to a MIMO system
supporting OFDM on the DL. OFDM is a spread-spectrum technique that
modulates data over a number of subcarriers within an OFDM symbol.
The subcarriers are spaced apart at precise frequencies. The
spacing provides "orthogonality" that enables a receiver to recover
the data from the subcarriers. In the time domain, a guard interval
(e.g., cyclic prefix) may be added to each OFDM symbol to combat
inter-OFDM-symbol interference. The UL may use SC-FDMA in the form
of a DFT-spread OFDM signal to compensate for high peak-to-average
power ratio (PAPR).
[0083] FIG. 3 is a diagram 300 illustrating an example of a DL
frame structure in a telecommunications system (e.g., LTE). A frame
(10 ms) may be divided into 10 equally sized sub-frames with
indices of 0 through 9. Each sub-frame may include two consecutive
time slots. A resource grid may be used to represent two time
slots, each time slot including a resource block. The resource grid
is divided into multiple resource elements. In LTE, a resource
block contains 12 consecutive subcarriers in the frequency domain
and, for a normal cyclic prefix in each OFDM symbol, 7 consecutive
OFDM symbols in the time domain, or 84 resource elements. For an
extended cyclic prefix, a resource block contains 6 consecutive
OFDM symbols in the time domain and has 72 resource elements. Some
of the resource elements, as indicated as R 302, 304, include DL
reference signals (DL-RS). The DL-RS include Cell-specific RS (CRS)
(also sometimes called common RS) 302 and UE-specific RS (UE-RS)
304. UE-RS 304 are transmitted only on the resource blocks upon
which the corresponding physical DL shared channel (PDSCH) is
mapped. The number of bits carried by each resource element depends
on the modulation scheme. Thus, the more resource blocks that a UE
receives and the higher the modulation scheme, the higher the data
rate for the UE.
[0084] In LTE, a NB may send a primary synchronization signal (PSS)
and a secondary synchronization signal (SSS) for each cell in the
BS. The primary and secondary synchronization signals may be sent
in symbol periods 6 and 5, respectively, in each of subframes 0 and
5 of each radio frame with the normal cyclic prefix (CP). The
synchronization signals may be used by UEs for cell detection and
acquisition. The NB may send a Physical Broadcast Channel (PBCH) in
symbol periods 0 to 3 in slot 1 of subframe 0. The PBCH may carry
certain system information.
[0085] The NB may send a Physical Control Format Indicator Channel
(PCFICH) in the first symbol period of each subframe. The PCFICH
may convey the number of symbol periods (M) used for control
channels, where M may be equal to 1, 2 or 3 and may change from
subframe to subframe. M may also be equal to 4 for a small system
bandwidth, e.g., with less than 10 resource blocks. The NB may send
a Physical HARQ Indicator Channel (PHICH) and a Physical Downlink
Control Channel (PDCCH) in the first M symbol periods of each
subframe. The PHICH may carry information to support hybrid
automatic repeat request (HARQ). The PDCCH may carry information on
resource allocation for UEs and control information for downlink
channels. The NB may send a Physical Downlink Shared Channel
(PDSCH) in the remaining symbol periods of each subframe. The PDSCH
may carry data for UEs scheduled for data transmission on the
downlink.
[0086] The NB may send the PSS, SSS, and PBCH in the center 1.08
MHz of the system bandwidth used by the NB. The NB may send the
PCFICH and PHICH across the entire system bandwidth in each symbol
period in which these channels are sent. The NB may send the PDCCH
to groups of UEs in certain portions of the system bandwidth. The
NB may send the PDSCH to specific UEs in specific portions of the
system bandwidth. The NB may send the PSS, SSS, PBCH, PCFICH, and
PHICH in a broadcast manner to all UEs, may send the PDCCH in a
unicast manner to specific UEs, and may also send the PDSCH in a
unicast manner to specific UEs.
[0087] A number of resource elements may be available in each
symbol period. Each resource element (RE) may cover one subcarrier
in one symbol period and may be used to send one modulation symbol,
which may be a real or complex value. Resource elements not used
for a reference signal in each symbol period may be arranged into
resource element groups (REGs). Each REG may include four resource
elements in one symbol period. The PCFICH may occupy four REGs,
which may be spaced approximately equally across frequency, in
symbol period 0. The PHICH may occupy three REGs, which may be
spread across frequency, in one or more configurable symbol
periods. For example, the three REGs for the PHICH may all belong
in symbol period 0 or may be spread in symbol periods 0, 1, and 2.
The PDCCH may occupy 9, 18, 36, or 72 REGs, which may be selected
from the available REGs, in the first M symbol periods, for
example. Only certain combinations of REGs may be allowed for the
PDCCH.
[0088] A UE may know the specific REGs used for the PHICH and the
PCFICH. The UE may search different combinations of REGs for the
PDCCH. The number of combinations to search is typically less than
the number of allowed combinations for the PDCCH. A NB may send the
PDCCH to the UE in any of the combinations that the UE will
search.
[0089] In other systems (e.g., such NR or 5G systems), a Node B may
transmit these or other signals in these locations or in different
locations of the subframe.
[0090] FIG. 4 is a diagram 400 illustrating an example of an UL
frame structure in a telecommunications system (e.g., LTE). The
available resource blocks for the UL may be partitioned into a data
section and a control section. The control section may be formed at
the two edges of the system bandwidth and may have a configurable
size. The resource blocks in the control section may be assigned to
UEs for transmission of control information. The data section may
include all resource blocks not included in the control section.
The UL frame structure results in the data section including
contiguous subcarriers, which may allow a single UE to be assigned
all of the contiguous subcarriers in the data section.
[0091] A UE may be assigned resource blocks 410a, 410b in the
control section to transmit control information to a BS. The UE may
also be assigned resource blocks 420a, 420b in the data section to
transmit data to the BS. The UE may transmit control information in
a physical UL control channel (PUCCH) on the assigned resource
blocks in the control section. The UE may transmit only data or
both data and control information in a physical UL shared channel
(PUSCH) on the assigned resource blocks in the data section. A UL
transmission may span both slots of a subframe and may hop across
frequency.
[0092] A set of resource blocks may be used to perform initial
system access and achieve UL synchronization in a physical random
access channel (PRACH) 430. The PRACH 430 carries a random sequence
and cannot carry any UL data/signaling. Each random access preamble
occupies a bandwidth corresponding to six consecutive resource
blocks. The starting frequency is specified by the network. That
is, the transmission of the random access preamble is restricted to
certain time and frequency resources. There is no frequency hopping
for the PRACH. The PRACH attempt is carried in a single subframe (1
ms) or in a sequence of few contiguous subframes and a UE can make
only a single PRACH attempt per frame (10 ms).
[0093] As will described in more detail below, in other systems
(e.g., NR or 5G systems), different uplink and/or downlink frame
structures may be used.
[0094] FIG. 5 is a diagram 500 illustrating an example of a radio
protocol architecture for the user and control planes in a
telecommunications system (e.g., LTE). The radio protocol
architecture for the UE and the BS is shown with three layers:
Layer 1, Layer 2, and Layer 3. Layer 1 (L1 layer) is the lowest
layer and implements various physical layer signal processing
functions. The L1 layer will be referred to herein as the physical
layer 506. Layer 2 (L2 layer) 508 is above the physical layer 506
and is responsible for the link between the UE and BS over the
physical layer 506.
[0095] In the user plane, the L2 layer 508 includes a media access
control (MAC) sublayer 510, a radio link control (RLC) sublayer
512, and a packet data convergence protocol (PDCP) 514 sublayer,
which are terminated at the BS on the network side. Although not
shown, the UE may have several upper layers above the L2 layer 508
including a network layer (e.g., IP layer) that is terminated at
the PDN gateway 118 on the network side, and an application layer
that is terminated at the other end of the connection (e.g., far
end UE, server, etc.).
[0096] The PDCP sublayer 514 provides multiplexing between
different radio bearers and logical channels. The PDCP sublayer 514
also provides header compression for upper layer data packets to
reduce radio transmission overhead, security by ciphering the data
packets, and handover support for UEs between BSs. The RLC sublayer
512 provides segmentation and reassembly of upper layer data
packets, retransmission of lost data packets, and reordering of
data packets to compensate for out-of-order reception due to hybrid
automatic repeat request (HARQ). The MAC sublayer 510 provides
multiplexing between logical and transport channels. The MAC
sublayer 510 is also responsible for allocating the various radio
resources (e.g., resource blocks) in one cell among the UEs. The
MAC sublayer 510 is also responsible for HARQ operations.
[0097] In the control plane, the radio protocol architecture for
the UE and BS is substantially the same for the physical layer 506
and the L2 layer 508 with the exception that there is no header
compression function for the control plane. The control plane also
includes a radio resource control (RRC) sublayer 516 in Layer 3 (L3
layer). The RRC sublayer 516 is responsible for obtaining radio
resources (i.e., radio bearers) and for configuring the lower
layers using RRC signaling between the BS and the UE.
[0098] FIG. 6 is a block diagram of a BS 610 in communication with
a UE 650 in an access network in accordance with aspects of the
present disclosure. The BSs of FIG. 1 and FIG. 2 may include one or
more components of BS 610 illustrated in FIG. 6. Similarly, the UEs
illustrated in FIGS. 1 and 2 may include one or more components of
UE 650 as illustrated in FIG. 6. One or more components of the UE
650 and BS 610 may be configured to perform the operations
described herein.
[0099] In the DL, upper layer packets from the core network are
provided to a controller/processor 675. The controller/processor
675 implements the functionality of the L2 layer. In the DL, the
controller/processor 675 provides header compression, ciphering,
packet segmentation and reordering, multiplexing between logical
and transport channels, and radio resource allocations to the UE
650 based on various priority metrics. The controller/processor 675
is also responsible for HARQ operations, retransmission of lost
packets, and signaling to the UE 650.
[0100] The TX processor 616 implements various signal processing
functions for the L1 layer (i.e., physical layer). The signal
processing functions includes coding and interleaving to facilitate
forward error correction (FEC) at the UE 650 and mapping to signal
constellations based on various modulation schemes (e.g., binary
phase-shift keying (BPSK), quadrature phase-shift keying (QPSK),
M-phase-shift keying (M-PSK), M-quadrature amplitude modulation
(M-QAM)). The coded and modulated symbols are then split into
parallel streams. Each stream is then mapped to an OFDM subcarrier,
multiplexed with a reference signal (e.g., pilot) in the time
and/or frequency domain, and then combined together using an
Inverse Fast Fourier Transform (IFFT) to produce a physical channel
carrying a time domain OFDM symbol stream. The OFDM stream is
spatially precoded to produce multiple spatial streams. Channel
estimates from a channel estimator 674 may be used to determine the
coding and modulation scheme, as well as for spatial processing.
The channel estimate may be derived from a reference signal and/or
channel condition feedback transmitted by the UE 650. Each spatial
stream is then provided to a different antenna 620 via a separate
transmitter 618TX. Each transmitter 618TX modulates an RF carrier
with a respective spatial stream for transmission.
[0101] At the UE 650, each receiver 654RX receives a signal through
its respective antenna 652. Each receiver 654RX recovers
information modulated onto an RF carrier and provides the
information to the receiver (RX) processor 656. The RX processor
656 implements various signal processing functions of the L1 layer.
The RX processor 656 performs spatial processing on the information
to recover any spatial streams destined for the UE 650. If multiple
spatial streams are destined for the UE 650, they may be combined
by the RX processor 656 into a single OFDM symbol stream. The RX
processor 656 then converts the OFDM symbol stream from the
time-domain to the frequency domain using a Fast Fourier Transform
(FFT). The frequency domain signal comprises a separate OFDM symbol
stream for each subcarrier of the OFDM signal. The symbols on each
subcarrier, and the reference signal, is recovered and demodulated
by determining the most likely signal constellation points
transmitted by the BS 610. These soft decisions may be based on
channel estimates computed by the channel estimator 658. The soft
decisions are then decoded and deinterleaved to recover the data
and control signals that were originally transmitted by the BS 610
on the physical channel. The data and control signals are then
provided to the controller/processor 659.
[0102] The controller/processor 659 implements the L2 layer. The
controller/processor 659 can be associated with a memory 660 that
stores program codes and data. The memory 660 may be referred to as
a computer-readable medium. In the UL, the controller/processor 659
provides demultiplexing between transport and logical channels,
packet reassembly, deciphering, header decompression, control
signal processing to recover upper layer packets from the core
network. The upper layer packets are then provided to a data sink
662, which represents all the protocol layers above the L2 layer.
Various control signals may also be provided to the data sink 662
for L3 processing. The controller/processor 659 is also responsible
for error detection using an acknowledgement (ACK) and/or negative
acknowledgement (NACK) protocol to support HARQ operations.
[0103] In the UL, a data source 667 is used to provide upper layer
packets to the controller/processor 659. The data source 667
represents all protocol layers above the L2 layer. Similar to the
functionality described in connection with the DL transmission by
the BS 610, the controller/processor 659 implements the L2 layer
for the user plane and the control plane by providing header
compression, ciphering, packet segmentation and reordering, and
multiplexing between logical and transport channels based on radio
resource allocations by the BS 610. The controller/processor 659 is
also responsible for HARQ operations, retransmission of lost
packets, and signaling to the BS 610.
[0104] Channel estimates derived by a channel estimator 658 from a
reference signal or feedback transmitted by the BS 610 may be used
by the TX processor 668 to select the appropriate coding and
modulation schemes, and to facilitate spatial processing. The
spatial streams generated by the TX processor 668 are provided to
different antenna 652 via separate transmitters 654TX. Each
transmitter 654TX modulates an RF carrier with a respective spatial
stream for transmission.
[0105] The UL transmission is processed at the BS 610 in a manner
similar to that described in connection with the receiver function
at the UE 650. Each receiver 618RX receives a signal through its
respective antenna 620. Each receiver 618RX recovers information
modulated onto an RF carrier and provides the information to a RX
processor 670. The RX processor 670 may implement the L1 layer.
[0106] The controller/processor 675 implements the L2 layer. The
controller/processor 675 can be associated with a memory 676 that
stores program codes and data. The memory 676 may be referred to as
a computer-readable medium. In the UL, the controller/processor 675
provides demultiplexing between transport and logical channels,
packet reassembly, deciphering, header decompression, control
signal processing to recover upper layer packets from the UE 650.
Upper layer packets from the controller/processor 675 may be
provided to the core network. The controller/processor 675 is also
responsible for error detection using an ACK and/or NACK protocol
to support HARQ operations.
[0107] The controller/processor 659 may direct the operation at the
UE 650. The controller/processor 659 and/or other processors,
components, and/or modules at the UE 650 may perform or direct
operations performed by the UE as described herein. The
controller/processor 675 may direct the operations at the BS 610.
The controller/processor 675 and/or other processors, components,
and/or modules at the BS 610 may perform or direct operations
performed by the BS as described herein. In aspects, one or more of
any of the components shown in FIG. 6 may be employed to perform
example operations 1300, 1400, 1700, and 1800 shown in FIGS. 13,
14, 17, and 18, respectively, and can also perform other UE and BS
operations for the techniques described herein.
[0108] For example, one or more of the antenna 620, transceiver
618, controller/processor, and memory 676 may be configured to
receive an uplink reference signal from a UE, measure the uplink
reference signal, and transmit a handover command, as described
herein. One or more of the antenna 652, transceiver 654,
controller/processor 659, and memory 660 may be configured to
transmit an uplink reference signal and receive a beamformed
downlink signal or handover command, as described herein.
Example NR/5G RAN Architecture
[0109] While aspects of the examples described herein may be
associated with LTE technologies, aspects of the present disclosure
may be applicable with other wireless communications systems, such
as NR or 5G technologies.
[0110] New radio (NR) may refer to radios configured to operate
according to a new air interface (e.g., other than Orthogonal
Frequency Divisional Multiple Access (OFDMA)-based air interfaces)
or fixed transport layer (e.g., other than Internet Protocol (IP)).
NR may utilize OFDM with a CP on the uplink and downlink and
include support for half-duplex operation using TDD. NR may include
Enhanced Mobile Broadband (eMBB) service targeting wide bandwidth
(e.g. 80 MHz beyond), millimeter wave (mmW) targeting high carrier
frequency (e.g. 60 GHz), massive MTC (mMTC) targeting non-backward
compatible MTC techniques, and/or mission critical targeting ultra
reliable low latency communications (URLLC) service.
[0111] A single component carrier bandwidth of 100 MHZ may be
supported. NR resource blocks may span 12 sub-carriers with a
sub-carrier bandwidth of 75 kHz over a 0.1 ms duration. Each radio
frame may consist of 50 subframes with a length of 10 ms.
Consequently, each subframe may have a length of 0.2 ms. Each
subframe may indicate a link direction (i.e., DL or UL) for data
transmission and the link direction for each subframe may be
dynamically switched. Each subframe may include DL/UL data as well
as DL/UL control data. UL and DL subframes for NR may be as
described in more detail below with respect to FIGS. 9 and 10.
[0112] Beamforming may be supported and beam direction may be
dynamically configured. MIMO transmissions with precoding may also
be supported. MIMO configurations in the DL may support up to 8
transmit antennas with multi-layer DL transmissions up to 8 streams
and up to 2 streams per UE. Multi-layer transmissions with up to 2
streams per UE may be supported. Aggregation of multiple cells may
be supported with up to 8 serving cells. Alternatively, NR may
support a different air interface, other than an OFDM-based
interface. NR networks may include entities such central units or
distributed units
[0113] The RAN may include a central unit (CU) and distributed
units (DUs). A NR BS (e.g., gNB, 5G Node B, Node B, transmission
reception point (TRP), access point (AP)) may correspond to one or
multiple BSs. NR cells can be configured as access cells (ACells)
or data only cells (DCells). For example, the RAN (e.g., a central
unit or distributed unit) can configure the cells. DCells may be
cells used for carrier aggregation or dual connectivity and may not
be used for initial access, cell selection/reselection, or
handover. In some cases DCells may not transmit synchronization
signals (SS)--in some case cases DCells may transmit SS. NR BSs may
transmit downlink signals to UEs indicating the cell type. Based on
the cell type indication, the UE may communicate with the NR BS.
For example, the UE may determine NR BSs to consider for cell
selection, access, handover, and/or measurement based on the
indicated cell type.
[0114] FIG. 7 illustrates an example logical architecture of a
distributed RAN 700, according to aspects of the present
disclosure. A 5G access node 706 may include an access node
controller (ANC) 702. The ANC may be a central unit (CU) of the
distributed RAN 700. The backhaul interface to the next generation
core network (NG-CN) 704 may terminate at the ANC. The backhaul
interface to neighboring next generation access nodes (NG-ANs) may
terminate at the ANC. The ANC may include one or more TRPs 708
(which may also be referred to as BSs, NR BSs, Node Bs, 5G NBs,
APs, or some other term). As described above, a TRP may be used
interchangeably with "cell."
[0115] The TRPs 708 may be a distributed unit (DU). The TRPs may be
connected to one ANC (ANC 702) or more than one ANC (not
illustrated). For example, for RAN sharing, radio as a service
(RaaS), and service specific AND deployments, the TRP may be
connected to more than one ANC. A TRP may include one or more
antenna ports. The TRPs may be configured to individually (e.g.,
dynamic selection) or jointly (e.g., joint transmission) serve
traffic to a UE.
[0116] The local architecture 700 may be used to illustrate
fronthaul definition. The architecture may be defined that support
fronthauling solutions across different deployment types. For
example, the architecture may be based on transmit network
capabilities (e.g., bandwidth, latency, and/or jitter).
[0117] The architecture may share features and/or components with
LTE. According to aspects, the next generation AN (NG-AN) 710 may
support dual connectivity with NR. The NG-AN may share a common
fronthaul for LTE and NR.
[0118] The architecture may enable cooperation between and among
TRPs 708. For example, cooperation may be preset within a TRP
and/or across TRPs via the ANC 702. According to aspects, no
inter-TRP interface may be needed/present.
[0119] According to aspects, a dynamic configuration of split
logical functions may be present within the architecture 700. The
PDCP, RLC, MAC protocol may be adaptably placed at the ANC or
TRP.
[0120] According to certain aspects, a BS may include a central
unit (CU) (e.g., ANC 702) and/or one or more distributed units
(e.g., one or more TRPs 708).
[0121] FIG. 8 illustrates an example physical architecture of a
distributed RAN 800, according to aspects of the present
disclosure. A centralized core network unit (C-CU) 802 may host
core network functions. The C-CU may be centrally deployed. C-CU
functionality may be offloaded (e.g., to advanced wireless services
(AWS)), in an effort to handle peak capacity.
[0122] A centralized RAN unit (C-RU) 804 may host one or more ANC
functions. Optionally, the C-RU may host core network functions
locally. The C-RU may have distributed deployment. The C-RU may be
closer to the network edge.
[0123] A distributed unit (DU) 706 may host one or more TRPs. The
DU may be located at edges of the network with radio frequency (RF)
functionality.
[0124] FIG. 9 is a diagram 900 showing an example of a DL-centric
subframe. The DL-centric subframe may include a control portion
902. The control portion 902 may exist in the initial or beginning
portion of the DL-centric subframe. The control portion 902 may
include various scheduling information and/or control information
corresponding to various portions of the DL-centric subframe. In
some configurations, the control portion 902 may be a physical DL
control channel (PDCCH), as indicated in FIG. 9. The DL-centric
subframe may also include a DL data portion 904. The DL data
portion 904 may sometimes be referred to as the payload of the
DL-centric subframe. The DL data portion 904 may include the
communication resources utilized to communicate DL data from the
scheduling entity (e.g., UE or BS) to the subordinate entity (e.g.,
UE). In some configurations, the DL data portion 904 may be a
physical DL shared channel (PDSCH).
[0125] The DL-centric subframe may also include a common UL portion
906. The common UL portion 906 may sometimes be referred to as an
UL burst, a common UL burst, and/or various other suitable terms.
The common UL portion 906 may include feedback information
corresponding to various other portions of the DL-centric subframe.
For example, the common UL portion 906 may include feedback
information corresponding to the control portion 902. Non-limiting
examples of feedback information may include an ACK signal, a NACK
signal, a HARQ indicator, and/or various other suitable types of
information. The common UL portion 906 may include additional or
alternative information, such as information pertaining to random
access channel (RACH) procedures, scheduling requests (SRs), and
various other suitable types of information. As illustrated in FIG.
9, the end of the DL data portion 904 may be separated in time from
the beginning of the common UL portion 906. This time separation
may sometimes be referred to as a gap, a guard period, a guard
interval, and/or various other suitable terms. This separation
provides time for the switch-over from DL communication (e.g.,
reception operation by the subordinate entity (e.g., UE)) to UL
communication (e.g., transmission by the subordinate entity (e.g.,
UE)). One of ordinary skill in the art will understand that the
foregoing is merely one example of a DL-centric subframe and
alternative structures having similar features may exist without
necessarily deviating from the aspects described herein.
[0126] FIG. 10 is a diagram 1000 showing an example of an
UL-centric subframe. The UL-centric subframe may include a control
portion 1002. The control portion 1002 may exist in the initial or
beginning portion of the UL-centric subframe. The control portion
1002 in FIG. 10 may be similar to the control portion 1002
described above with reference to FIG. 9. The UL-centric subframe
may also include an UL data portion 1004. The UL data portion 1004
may sometimes be referred to as the payload of the UL-centric
subframe. The UL portion may refer to the communication resources
utilized to communicate UL data from the subordinate entity (e.g.,
UE) to the scheduling entity (e.g., UE or BS). In some
configurations, the control portion 1002 may be a physical UL
shared channel (PUSCH).
[0127] As illustrated in FIG. 10, the end of the control portion
1002 may be separated in time from the beginning of the UL data
portion 1004. This time separation may sometimes be referred to as
a gap, guard period, guard interval, and/or various other suitable
terms. This separation provides time for the switch-over from DL
communication (e.g., reception operation by the scheduling entity)
to UL communication (e.g., transmission by the scheduling entity).
The UL-centric subframe may also include a common UL portion 1006.
The common UL portion 1006 in FIG. 10 may be similar to the common
UL portion 1006 described above with reference to FIG. 10. The
common UL portion 1006 may additional or alternative include
information pertaining to channel quality indicator (CQI), sounding
reference signals (SRSs), and various other suitable types of
information. One of ordinary skill in the art will understand that
the foregoing is merely one example of an UL-centric subframe and
alternative structures having similar features may exist without
necessarily deviating from the aspects described herein.
[0128] In some circumstances, two or more subordinate entities
(e.g., UEs) may communicate with each other using sidelink signals.
Real-world applications of such sidelink communications may include
public safety, proximity services, UE-to-network relaying,
vehicle-to-vehicle (V2V) communications, Internet of Everything
(IoE) communications, IoT communications, mission-critical mesh,
and/or various other suitable applications. Generally, a sidelink
signal may refer to a signal communicated from one subordinate
entity (e.g., UE.sub.1) to another subordinate entity (e.g.,
UE.sub.2) without relaying that communication through the
scheduling entity (e.g., UE or BS), even though the scheduling
entity may be utilized for scheduling and/or control purposes. In
some examples, the sidelink signals may be communicated using a
licensed spectrum (unlike wireless local area networks, which
typically use an unlicensed spectrum)
Example Downlink-Based Mobility Procedure
[0129] FIG. 11 illustrates an example call-flow diagram
illustrating operations 1100 which may be performed in a handover
procedure, according to certain wireless technologies. For example,
in a 4G communication system, a UE 1102 synchronizes to a source BS
1104. At 1108, the source BS 1104 provides (e.g., transmits) a
measurement configuration to the UE 1102. The measurement
configuration may include one or more of the cells on which the UE
1102 may perform measurements, criteria used by the UE 1102 to
trigger a transmission of a measurement report, and/or the
measurements that the UE 1102 may perform.
[0130] At 710, the UE 1102 measures downlink signals transmitted by
a target BS 1106 according to the received measurement
configuration. For example, the UE 1102 may measure cell specific
reference signals (CRS) transmitted by the target BS 706 in an
effort to determine downlink channel quality. A handover trigger
1112 occurs based, at least in part, on the UE downlink signal
measurements. For example, the handover trigger at 1112 may occur
upon determining the downlink channel quality associated with the
target BS 1106 exceeds the downlink channel quality associated with
the source BS 1104.
[0131] In response to the handover trigger, at 1114, the UE 1102
transmits a status request (SR) message to the source BS 1104. The
source BS 114 transmits an uplink allocation at 1116 to the UE
1102. The UE 1102 transmits a measurement report at 1118 using the
received uplink allocation. At 1120, the source BS 1104 and target
BS 1106 exchange information and make a handover decision regarding
the UE 1102 based on the received measurement report. Accordingly,
the handover decision may be based, at least in part, on downlink
signal measurements taken by the UE 1102.
[0132] Based on the handover decision at 1120, the source BS 1104
transmits, at 1122, a radio resource control (RRC) connection
reconfiguration message, indicating a request to modify an RRC
connection and perform a handover to the target BS 1106. After
receiving the handover command, the UE 1102, at 1124, performs a
random access procedure with the target BS 1106. At 1126, the UE
1102 receives a random access response and uplink allocation from
the target BS 1106. At 1128, the UE 1102 transmits an RRC
connection reconfiguration complete message to the target BS 1106,
confirming completion of the RRC connection reconfiguration.
Example Uplink-Based Mobility
[0133] As described above, handover decisions may be based on
measurements of received downlink signals (e.g., downlink-based
mobility). In an effort to perform handovers in a user-centric
environment, it may be desirable to perform handovers based, at
least in part, on uplink signal measurements taken by BSs. For
example, NR/5G and other future communication systems may focus on
creating a more user-centric network. User-centric networking may
refer the use of user devices in autonomic and self-organizing
wireless community networks, for example, created and controlled by
the user.
[0134] FIG. 12 is an example call-flow diagram illustrating
operations 1200 which may be performed in a handover procedure,
according to certain aspects of the present disclosure. At 1208,
the source BS 1204 provides the UE 1202 with a configuration for an
uplink reference signal to be transmitted by the UE 1202. This
uplink reference signal, which may be referred to as a "chirp", may
be advantageously received by both the source BS 1204 and one or
more target BS 1206.
[0135] Although not shown in FIG. 12, the source BS 1204 and target
BS 1206 may exchange information regarding the UE 1202 (e.g., via
an X2 interface or backhaul connection), in an effort to facilitate
the target BS 1206 detecting the uplink reference signal. For
example, the target BS 1206 may receive a UE ID and/or reference
signal configuration (e.g., chirp configuration) from the source BS
1204. In this manner, the target BS 1206 may be aware of the UE
1202 and may detect the uplink reference signal.
[0136] According to certain aspects, though not illustrated in FIG.
12, power control commands may be received by the UE 1202 for the
uplink reference signal. For example, the source BS 1204 may
transmit power control commands for the uplink reference signal in
an effort for the target BS 1206 to receive the uplink reference
signal.
[0137] According to certain aspects, the uplink reference signal
may include a cyclic prefix (CP) configuration which may assist the
target BS 1206 in detecting the chirp signal. Since uplink signals
may be time-aligned with the source BS 1204, allowing a special CP
configuration for the chirp signal may increase chances of
reception by the target BS.
[0138] As compared to the handover procedure illustrated in FIG.
11, aspects described herein allow a handover decision to be made
based on uplink reference signal measurements taken by the source
BS 1204 and the target BS 1206. In this manner, as will be
described with reference to FIG. 12, the UE 1202 receives a "keep
alive" (KA)/handover command or a RRC connection reconfiguration
message from the target BS 1206, as opposed to receiving the RRC
connection reconfiguration message from the source BS 1204.
[0139] At 1210, the UE 1202 transmits an uplink reference signal,
in accordance with the received chirp configuration, capable of
being received by both the source BS 1204 and the target BS 1206.
The source BS 1204 and the target BS 1206 measure the received
uplink reference signal. At 1212, the source BS 1204 and the target
BS 1206 may collectively decide to handover the UE 1202 from the
source BS 1204 to the target BS 1206 based on uplink measurements
of the chirp signal.
[0140] At 1214, either the source BS 1204 or the target BS 1206 may
transmit a KA/handover command to the UE 1202, indicating a
handover is to be performed. According to certain aspects, the
KA/handover message may be scrambled by a UE identifier, as opposed
to, for example, a cell identification. Scrambling by the UE
identifier enables the target BS 1206 to transmit the KA/handover
command at 1214. The KA/handover message may include the target
BS's cell identification and timing advance (TA). According to
certain aspects, the target BS 1206 may determine the TA based on
the received uplink reference signal. Additionally, the KA/handover
command 1214 may include an uplink/downlink allocation for the
target BS 1206 and UE 1202. In this manner, the UE 1202 may begin
communicating with the target BS 1206 after receiving the
KA/handover command.
[0141] At 1216, at least one of the source BS 1204 or the target BS
1206 may transmit an RRC connection reconfiguration message
indicating a request to modify an RRC connection. For example, the
BS which initiates the handover may transmit the RRC connection
reconfiguration message. At 1218, the UE 1202 transmits an RRC
connection reconfiguration complete message to the target BS
1206.
[0142] As described above, an uplink reference signal transmitted
by the UE 1202 allows the source BS 1204 and one or more potential
target BS 1206 to measure uplink signal strength. The uplink
reference signal may be an RRC dedicated uplink reference signal.
According to aspects, the uplink reference signal may be an uplink
wide-band signal.
[0143] FIG. 13 illustrates example operations 1300 which may be
performed by a UE (e.g., UE 110), according to aspects of the
present disclosure. The operations may be performed by one or more
components of UE 650 illustrated in FIG. 6. For example, one or
more of the antenna 652, transceiver 654, controller/processor 659,
and memory 660 may be configured to perform the operations
illustrated in FIG. 13.
[0144] At 1302, the UE may be configured to transmit an uplink
reference signal. At 1304, the UE may be configured to receive a
handover command based, at least in part, on the uplink reference
signal. At 1306, the UE may be configured to take one or more
actions to perform a handover to a target BS in accordance with the
handover command.
[0145] As described above, the UE may receive a configuration for
the uplink reference signal from a serving BS, wherein the
configuration allows the target BS to receive the uplink reference
signal. Advantageously, the handover command may be received from a
serving BS or a target BS. The handover command may be scrambled by
a UE identifier (as opposed to a cell ID). Similar to the handover
command, a connection reconfiguration message may be received from
one of the serving BS or the target BS.
[0146] The handover command may include one or more of a cell
identification associated with a target BS, a timing advance (TA)
associated with the target BS, or an uplink/downlink resource
allocation for communicating with the target BS.
[0147] The UE may receive a power control command from the serving
BS for the uplink reference signal and may transmit the uplink
reference signal in accordance with received power control
command.
[0148] As described above, a cyclic prefix (CP) of the uplink
reference signal may be longer than a CP is longer than a CP of
another type of reference signal, in an effort to assist the target
BS to detect the uplink reference signal.
[0149] FIG. 14 illustrates example operations 1400 which may be
performed by a first BS, such as a BS serving a UE or a non-serving
BS, according to aspects of the present disclosure. The operations
may be performed by one or more components of BS 610 illustrated in
FIG. 6. For example, one or more of the antenna 620, transceiver
618, controller/processor 675, and memory 676 may be configured to
perform the operations 1400.
[0150] At 1402, the BS may receive an uplink reference signal from
a user equipment (UE). At 1404, the BS may measure the uplink
reference signal. At 1406, the BS may transmit a handover command
to the UE based, at least in part, on the measured uplink reference
signal.
[0151] The serving BS may transmit, to the UE, a configuration for
the uplink reference signal, wherein the configuration allows a
second, non-serving BS to receive the uplink reference signal.
[0152] A non-serving BS (e.g., a target BS) may receive, from the
serving BS, a configuration for the uplink reference signal,
wherein the configuration allows the non-serving BS to receive the
uplink reference signal.
[0153] As described above, either the serving or non-serving BS may
transmit a connection reconfiguration message to the UE.
[0154] Aspects described herein allow support for forward and
backward handover using an uplink reference signal. For example, a
forward handover may refer to a handover where a UE receives the
handover command directly from a target BS. According to one
example of a forward handover, with reference to FIG. 1, a UE 110
communicating with a source BS 132 may handover to a target BS 122
without the source BS 132 first preparing the target BS 122 for the
handover. A backward handover may refer to a handover wherein the
UE receives a handover command from the serving BS. By using an
uplink signal which may be received by a serving and non-serving
BS, aspects of the present disclosure allow handover decisions to
be made using measurement of the uplink reference signal.
Example Beam Selection for Uplink and Downlink Based Mobility
[0155] In some cases, advanced radio-access technology (RAT)
networks (e.g., 5G systems and beyond) may be deployed with
multiple base stations (BSs) (e.g., transmission reception Points
(TRPs), gNBs, new radio (NR) BSs, access points (APs), Node Bs
(NBs), 5G NBs, etc.), for example, such as BS 122. In such cases,
data may be beamformed via the BSs.
[0156] In such advanced RAT networks, there may be two general
types of mobility procedures: uplink-based and downlink-based
mobility procedures. For the uplink based case, a UE (e.g., UE 110)
may send an uplink reference signal (e.g., such as the UE chirp,
described herein and also referred to as an uplink synchronization
signal (USS), uplink mobility indication channel (UMICH), or uplink
reference signal (URS)) and the network (e.g., BS) may measure the
uplink reference signals and make a mobility decision based on the
measurement. On the other hand, for the downlink-based case, the
network sends downlink reference signals (e.g., measurement
reference signals (MRS)) and UE measures the downlink reference
signals and sends a measurement report message including the
measured results of the downlink reference signals when certain
reporting criteria are met.
[0157] Aspects of the present disclosure provide mechanisms for
beam based wireless communication systems that may help efficiently
perform a beam selection with UL based techniques, DL based
techniques, or a "hybrid" combination of both UL and DL based
techniques.
[0158] Beam-based mobility procedures (e.g., to select different
beams based on channel conditions) may be implemented using a
variant of existing mobility procedures, but repeated with
(reference signals transmitted using) different beams. For example,
starting from primary synchronization signal (PSS) and/or secondary
synchronization signal (SSS) to subsequent signals based on
transmit/receive (Tx/Rx) beam pairs.
[0159] Aspects of the present disclosure provide a beam selection
mechanism for such RAT networks for downlink-based, uplink-based,
and hybrid uplink-downlink-based mobility scenarios.
Example Beam Selection for Uplink-Based Mobility
[0160] For UL based mobility (which may also be referred to as
UE-Centric Mobility as it is based on UL reference signals
transmitted by a UE), design targets may be reduced network RS
transmission for energy saving, improved handover reliability,
reduced handover frequency, and improved UE power saving.
[0161] FIG. 15 is an example state diagram illustrating example
UE-centric uplink-based mobility, in accordance with the
disclosure. As illustrated in FIG. 15, the UE (e.g., UE 110) can
perform an initial connection procedure at 1502-1514. The UE may be
in an RRC_IDLE state during the initial access. In the RRC_IDLE
state, the UE may have no dedicated resources. The UE may monitor a
paging channel with a long discontinuous reception (DRX) cycle
(e.g., around 320 ms-2560 ms). The UE can receive multimedia
broadcast multicast service (MBMS) data while in this state. Cell
selection can be performed for the initial access.
[0162] As shown in FIG. 15, at 1502, the UE monitors the
synchronization channel found during cell selection, for example,
for a primary synchronization signal (PSS) or secondary SS (SSS).
Once the UE is synchronized, the UE can receive physical broadcast
channel (PBCH) and system information (SI) at 1504. At 1506, the UE
sends an uplink reference signal (e.g., chirp) and, at 1508,
receives a "keep alive" (KA). The KA can indicate whether the
network has data for the UE (e.g., paging indicator=TRUE or FALSE).
At 1510, the UE may receive connection setup information, for
example, which may include the information to decode dedicated
channel information, such as cell-ID, C-RNTI, timing advance (TA)
information and/or resource allocation (RA) information for the UE.
The UE can use the allocated resources to transmit an RRC
connection request message at 1512. At 1514, the UE can receive the
RRC connection setup from the BS. This may complete initial access
and the UE may enter the RRC dedicated state, which may also be
referred to as the RRC_CONNECTED mode.
[0163] In the RRC dedicated state, the UE may perform the steps
1516-1522 illustrated in FIG. 15. In RRC dedicated state, the UE
may have C-RNTI and dedicated resources. In the RRC dedicated
state, for network controlled mobility, the UE monitors KA signals
(e.g., a physical layer (PHY) signal) with a short DRX cycle (e.g.,
2 ms-640 ms), sends uplink reference signals (and also CQI), and
uses a TA. The resource for the uplink reference signal may be UE
specific resource (e.g., similar to sounding reference signal)
assigned by the BS. As shown in FIG. 15, at 1516, the UE receives
radio resource management (RRM) configuration information from the
BS. The RRM configuration information may relate to a mobility
configuration for the UE. At 1518, the UE sends the uplink
reference signal according to the RRM configuration information. At
1520, the UE monitors for the KA signal. If the KA signal indicates
data for the UE, the UE monitors the downlink channel. At 1522, the
UE may receive a handover command in the downlink channel. In this
case, the UE remains in the RRC dedicated state and may repeat the
steps 1516-1522 with the new (e.g., target) BS after the handover.
On the other hand, if the KA signal does not indicate paging for
the UE (e.g., after a period of inactivity), then the UE may
receive a state transition command at 1524 and transition to the
RRC common state. The RRC common state may also be referred to as
the RRC inactive state, the RRC DORMANT state, or the Energy
Conserved Operation (ECO) state. The RRC common or RRC inactive
state may be a substrate of the RRC_CONNECTED state or of the
RRC_IDLE suspend mode. The terms may be used interchangeably.
[0164] In the RRC common state or RRC inactive state, the UE may
perform the steps 1526-1532 illustrated in FIG. 15. In the RRC
common state, the UE may have RRC common radio network temporary
identifier (RC-RNTI, e.g., Z-RNTI or C-RNTI) and common resources
(e.g., rather than dedicated resources). In the RRC common state
the network can control serving node changes. As shown in FIG. 15,
at 1526, the UE monitors for synchronization and, at 1528 sends an
uplink reference signal. The uplink reference signal may include a
UE-ID and/or a buffer status report (BSR) of the UE. The UE may
stay in the RRC common state until it receives a KA signal, at
1530, that indicates activity for the user (or the UE has data to
transmit), at which time the UE may perform connection setup at
1532 to transition to the RRC_CONNECTED state. As illustrated, in
RRC common state, the uplink reference signal may be used to make
serving node change decisions. For example, the KA signal may
indicate the paging indication and the UE may repeat the steps
1526-1530 until the KA signal indicates user plane activity for the
UE. If serving cell change takes place, the network may
autonomously change the serving cell without indicating paging
indicator=TRUE for the HO command.
[0165] According to certain aspects, for uplink-based mobility, the
handover decision (transmission point selection) by the BS may be
based on measurement of the uplink reference signal from the UE.
For uplink-based mobility, the BS may not send measurement
reference signals (MRS) to the UE. Beam selection may also be
performed by the BS based on the uplink reference signal from the
UE.
[0166] FIG. 16 is an example call flow diagram 1600 illustrating
beam selection for uplink-based mobility, in accordance with
aspects of the present disclosure. The call flow 1600 is more
generalized version of the state diagram shown in FIG. 15 for
uplink-based mobility, and also shows the beam selection (not shown
in FIG. 15). As shown in FIG. 16, at 1606, the UE 1602 can monitor
synchronization signals for acquisition (e.g., shown in FIG. 15).
The synchronization signals may include PSS, SSS, and/or zone SS
(ZSS). At 1608, the UE 1602 sends uplink reference signals which
may optionally include UE_ID. The uplink reference signals may be
similar to Msg 1 and Msg 3 signaling of a random access (RA)
procedure in the LTE system. At 1610, the UE 1602 receives a KA
signal (e.g., with PI=TRUE) from the BS 1604. Optionally, 1610a,
after receiving the KA signal, the UE 1602 receives a Physical Cell
Identity Channel (PCICH) indicting a cell-ID. At 1612, the UE 1602
receives C-RNTI, timing advance (TA) and/or uplink grant from the
BS 1604. This may be similar to Msg 2 and Msg 4 of the RA
procedure. At 1615, the UE 1602 and BS 1604 can exchange addition
signaling similar to the conventional LTE signaling performed after
Msg 4 (e.g., completion of the RA procedure) and information
configuring the uplink reference signal.
[0167] At 1616, the UE 1602 can transmit uplink reference signal(s)
to the BS 1604. The BS 1604 can measure the uplink reference
signal(s) from the UE 1602 and, at 1618, select the downlink beam
and/or BS based on the measurements. At 1620, the UE 1602 and BS
1604 can transmit uplink and/or downlink data. In addition, channel
state feedback (CSF) can be transmitted.
Example Beam Selection for Downlink-Based Mobility
[0168] FIG. 17 illustrates example operations 1700 for beam
selection for downlink-based mobility, in accordance with certain
aspects of the disclosure. The operations 1700 may be performed by
a UE (e.g., UE 110). The operations 1700 may be performed by one or
more components of UE 650 illustrated in FIG. 6. For example, one
or more of the antenna 652, transceiver 654, controller/processor
659, and memory 660 may be configured to perform the operations
1700.
[0169] At 1702, the UE transmits an uplink reference signal with an
indication of a preferred downlink beam. The uplink reference
signal may include a UE ID. In some cases, the preferred beam may
be selected (and the uplink reference signal transmitted) during a
connection establishment procedure. Alternatively, the uplink
reference signal with the preferred beam may be transmitted after
completion of the connection establishment procedure. The selection
of the preferred beam may be based on MRSs received from the
BS.
[0170] At 1704, the UE receives a downlink transmission based, at
least in part, on the uplink reference signal. For example, the UE
can receive beamformed downlink transmissions based on the
preferred beam or the UE can receive a handover command based on
the uplink reference signal.
[0171] FIG. 18 illustrates example operations 1800 for beam
selection for downlink-based mobility, according to aspects of the
present disclosure. The operations 1800 may be performed by a BS
such as BS 122. The operations 1800 may be performed by one or more
components of BS 610 illustrated in FIG. 6. For example, one or
more of the antenna 620, transceiver 618, controller/processor 675,
and memory 676 may be configured to perform the operations 1800.
The operations 1800 may be complementary operations performed by
the BS to the operations 1700 performed by the UE.
[0172] At 1802, the BS receives an uplink reference signal with an
indication of a preferred downlink beam. At 1804, the BS transmits
a downlink transmission based, at least in part, on the uplink
reference signal.
[0173] FIGS. 19 and 20 illustrate example call flow diagrams for
beam selection for downlink-based mobility. For DL-based mobility,
the network relies on feedback provided from the UE after measuring
MRS (measurement reference signals). In some cases, the MRS may be
transmitted using different beams, such that the feedback is used
to select a preferred beam for DL transmissions. According to
certain aspects, in an inter-BS beam management scheme, multiple
different beams may be transmitted by multiple different BSs.
Example Beam Selection During Initial Access
[0174] According to certain aspects, the UE can send an uplink
reference signal with an indication of preferred downlink beam
(e.g., or an index of suitable downlink beams) during initial
access. For example, the uplink reference signal can be in the
first message sent from the UE to the BS.
[0175] As shown in FIG. 19, at 1906, the UE 1902 can monitor
synchronization signals for acquisition. For downlink-based
mobility case, at 1908, the BS 1904 sends reference signals (e.g.,
MRS) to the UE 1902. In the example illustrated in FIG. 19, the MRS
are sent during initial access. The MRS may use different beams,
such that the UE 1902 can measure the MRS and select a preferred
beam and/or a preferred BS, at 1910. In some cases, the UE 1502 may
receive the MRS using different beamforming from multiple BSs Then,
at 1912, during the initial access (e.g., in the first message from
the UE 1902 to the BS 1904), the UE 1902 sends an uplink reference
signal with an indication of the preferred downlink beam and/or BS.
In some cases, the indication of the preferred beam may be an index
of suitable downlink beams. The uplink reference signal may
optionally include UE_ID.
[0176] At 1914, the UE 1902 receives a KA signal (e.g., with
PI=TRUE) from the BS 1904. Optionally, 1914a, after receiving the
KA signal, the UE 1902 receives a Physical Cell Identity Channel
(PCICH) indicting a cell-ID. At 1916, the UE 1902 receives C-RNTI,
TA and uplink grant from the BS 1904. At 1918, the UE 1902 and BS
1904 can exchange addition signaling similar to the conventional
LTE signaling performed after Msg 4 (e.g., completion of the RA
procedure) and information configuring the uplink reference signal.
At 1920, the UE 1902 and BS 1904 can exchange uplink and downlink
data and possibly CSF. The downlink data from the BS 1904 may be
beamformed according to the preferred beam indicated by the UE
1902. The BS 1904 can also make mobility decisions and send a
handover command based on the uplink reference signal, such as
based on the indication of the preferred beam and/or BS.
[0177] As illustrated in FIG. 19, beam selection may continue after
initial connection. At 1922, further transmissions of uplink
reference signals from the UE 1902 (with an indication of a
preferred downlink beam and/or BS) and MRS from the BS 1904 may
occur. The transmissions may be periodic and may have different
configured periodicities. The further MRS and uplink reference
signals can be used to optimize the beam selection.
Example Beam Selection after Initial Access
[0178] According to certain aspects, the MRS measurement and beam
selection may not occur until after completion of the initial
access procedure as shown in FIG. 16.
[0179] As shown in FIG. 20, the initial transmissions 2006-2014 may
similar to the transmissions at 1606-1614 for the uplink-based
mobility procedure illustrated in FIG. 16. At 2006, the UE 2002 can
monitor synchronization signals for acquisition. At 2008, the UE
2002 sends an uplink reference signal which may optionally include
UE ID--but does not include the indication of the preferred
downlink beam and/or transmission reception point.
[0180] At 2010, the UE 2002 receives a KA signal (e.g., with
PI=TRUE) from the BS 2004. Optionally, 2010a, after receiving the
KA signal, the UE 2010 receives a Physical Cell Identity Channel
(PCICH) indicting a cell-ID. At 2012, the UE 2002 receives TA and
uplink grant from the BS 2004. At 2014, the UE 2002 and BS 2004 can
exchange addition signaling similar to the conventional LTE
signaling performed after Msg 4 (e.g., completion of the RA
procedure) and information configuring the uplink reference
signal.
[0181] After the initial access procedure is completed, at 2016,
the BS 2004 sends reference signals (e.g., MRS) to the UE 2002. In
some cases, multiple BSs may send reference signals to the UE 2002.
The UE 2002 can measure the MRS and select a preferred beam and/or
a preferred BS, at 2018. Then, at 2020, the UE 2002 sends an uplink
reference signal with the indication of the preferred downlink beam
and/or BS.
[0182] At 2022, the UE 2002 and BS 2004 can exchange uplink and
downlink data and possibly CSF. The downlink data from the BS 2004
may be beamformed according to the preferred downlink beam
indicated by the UE 2002. The BS 2004 can also make mobility
decisions and send a handover command based on the uplink reference
signal, such as based on the indication of the preferred beam
and/or BS. At 2022, further transmissions of uplink reference
signals from the UE 2002 (with an indication of a preferred
downlink beam and/or BS) and MRS from the BS 2004 may occur. The
transmissions may be periodic and may have different configured
periodicities. The further MRS and uplink reference signals can be
used to optimize the beam selection.
Example Beam Selection for Hybrid Uplink-Downlink-Based
Mobility
[0183] According to certain aspects a hybrid uplink and downlink
based mobility and beam selection approach may be used. In the
hybrid approach, transmission reception point and/or beam selection
decisions can be based on both uplink and downlink reference
signals. For example, similar to uplink-based mobility, mobility
(e.g., handover) decisions by the BS can be based on the uplink
reference signal. However, the beam selection can be done by the UE
and included in the uplink reference signal and based on
measurement of MRS with different beams transmitted by the BS.
[0184] It is understood that the specific order or hierarchy of
steps in the processes disclosed is an illustration of exemplary
approaches. Based upon design preferences, it is understood that
the specific order or hierarchy of steps in the processes may be
rearranged. Further, some steps may be combined or omitted. The
accompanying method claims present elements of the various steps in
a sample order, and are not meant to be limited to the specific
order or hierarchy presented.
[0185] As used herein, a phrase referring to "at least one of" a
list of items refers to any combination of those items, including
single members. As an example, "at least one of: a, b, or c" is
intended to cover a, b, c, a-b, a-c, b-c, and a-b-c, as well as any
combination with multiples of the same element (e.g., a-a, a-a-a,
a-a-b, a-a-c, a-b-b, a-c-c, b-b, b-b-b, b-b-c, c-c, and c-c-c or
any other ordering of a, b, and c).
[0186] The previous description is provided to enable any person
skilled in the art to practice the various aspects described
herein. Various modifications to these aspects will be readily
apparent to those skilled in the art, and the generic principles
defined herein may be applied to other aspects. Thus, the claims
are not intended to be limited to the aspects shown herein, but is
to be accorded the full scope consistent with the language claims,
wherein reference to an element in the singular is not intended to
mean "one and only one" unless specifically so stated, but rather
"one or more." Unless specifically stated otherwise, the term
"some" refers to one or more. All structural and functional
equivalents to the elements of the various aspects described
throughout this disclosure that are known or later come to be known
to those of ordinary skill in the art are expressly incorporated
herein by reference and are intended to be encompassed by the
claims. Moreover, nothing disclosed herein is intended to be
dedicated to the public regardless of whether such disclosure is
explicitly recited in the claims. No claim element is to be
construed as a means plus function unless the element is expressly
recited using the phrase "means for."
* * * * *