U.S. patent application number 16/430016 was filed with the patent office on 2019-09-19 for enhanced cell acquisition for enhanced machine type communications.
The applicant listed for this patent is QUALCOMM Incorporated. Invention is credited to Wanshi CHEN, Seyed Ali Akbar FAKOORIAN, Alberto RICO ALVARINO, Hao XU.
Application Number | 20190289559 16/430016 |
Document ID | / |
Family ID | 55588611 |
Filed Date | 2019-09-19 |
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United States Patent
Application |
20190289559 |
Kind Code |
A1 |
RICO ALVARINO; Alberto ; et
al. |
September 19, 2019 |
ENHANCED CELL ACQUISITION FOR ENHANCED MACHINE TYPE
COMMUNICATIONS
Abstract
Aspects of the present disclosure provide techniques that may be
used by a BS and/or UE to reduce the time associated with
performing cell acquisition. An exemplary method, performed by a
BS, generally includes determining opportunities for assisting cell
acquisition by one or more UEs, and boosting transmission power for
one or more signals used for cell acquisition during the determined
opportunities. Another exemplary method, performed by a UE,
generally includes exiting a first low power state in order to
perform cell acquisition based on one or more signals transmitted
by a base station, and taking one or more actions to reduce
acquisition time when performing the cell acquisition.
Inventors: |
RICO ALVARINO; Alberto; (San
Diego, CA) ; CHEN; Wanshi; (San Diego, CA) ;
XU; Hao; (Beijing, CN) ; FAKOORIAN; Seyed Ali
Akbar; (San Diego, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
QUALCOMM Incorporated |
San Diego |
CA |
US |
|
|
Family ID: |
55588611 |
Appl. No.: |
16/430016 |
Filed: |
June 3, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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15063791 |
Mar 8, 2016 |
10321417 |
|
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16430016 |
|
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|
62142935 |
Apr 3, 2015 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
Y02D 70/1264 20180101;
H04W 52/0225 20130101; H04W 52/44 20130101; Y02D 70/1242 20180101;
Y02D 70/146 20180101; H04W 52/38 20130101; Y02D 70/26 20180101;
Y02D 30/70 20200801; H04B 17/318 20150115; H04B 17/23 20150115;
H04W 52/143 20130101; H04W 52/18 20130101; Y02D 70/142 20180101;
H04W 48/12 20130101; H04W 76/28 20180201; Y02D 70/24 20180101; Y02D
70/1262 20180101; H04W 48/20 20130101; Y02D 70/21 20180101 |
International
Class: |
H04W 52/38 20060101
H04W052/38; H04B 17/318 20060101 H04B017/318; H04W 48/12 20060101
H04W048/12; H04W 52/02 20060101 H04W052/02; H04W 52/14 20060101
H04W052/14; H04W 52/18 20060101 H04W052/18; H04W 52/44 20060101
H04W052/44; H04B 17/23 20060101 H04B017/23 |
Claims
1. A method for wireless communications by a user equipment (UE),
comprising: exiting a first low power state in order to perform
cell acquisition based on one or more signals transmitted by a base
station; and taking one or more actions to reduce acquisition time
when performing the cell acquisition.
2. The method of claim 1, further comprising: receiving an
announcement with information regarding opportunities when the one
or more signals will be transmitted with boosted transmission
power; and wherein taking the one or more actions comprises
coordinating exiting the first low power state based on the
information in the announcement.
3. The method of claim 2, further comprising: exiting a second low
power state to monitor for one or more signals, based on cell
acquisition already performed during one of the announced
opportunities.
4. The method of claim 1, wherein taking the one or more actions
comprises performing cell acquisition while monitoring for a
reduced set of synchronization signals, wherein the reduced set is
based at least in part on a previously determined cell ID.
5. The method of claim 4, wherein monitoring for the reduced set of
synchronization signals comprises searching for timing of a primary
synchronization signal (PSS) and secondary synchronization signal
(SSS) corresponding to the previously determined cell ID.
6. The method of claim 1, wherein taking the one or more actions
comprises: terminating the cell acquisition based on one or more
signal quality measurements; and returning to the first low power
state after terminating the cell acquisition.
7. The method of claim 1, wherein the one or more signals comprise
at least one of a primary synchronization signal (PSS), a secondary
synchronization signal (SSS), or a physical broadcast channel
(PBCH).
8. An apparatus for wireless communications, comprising: means for
exiting a first low power state in order to perform cell
acquisition based on one or more signals transmitted by a base
station; and means for taking one or more actions to reduce
acquisition time when performing the cell acquisition.
9. The apparatus of claim 8, further comprising: means for
receiving an announcement with information regarding opportunities
when the one or more signals will be transmitted with boosted
transmission power; and wherein the means for taking the one or
more actions comprises means for coordinating exiting the first low
power state based on the information in the announcement.
10. The apparatus of claim 9, further comprising: means for exiting
a second low power state to monitor for one or more signals, based
on cell acquisition already performed during one of the announced
opportunities.
11. The apparatus of claim 8, wherein the means for taking the one
or more actions comprises means for performing cell acquisition
while monitoring for a reduced set of synchronization signals,
wherein the reduced set is based at least in part on a previously
determined cell ID.
12. The apparatus of claim 11, wherein monitoring for the reduced
set of synchronization signals comprises means for searching for
timing of a primary synchronization signal (PSS) and secondary
synchronization signal (SSS) corresponding to the previously
determined cell ID.
13. The apparatus of claim 8, wherein the means for taking the one
or more actions comprises: means for terminating the cell
acquisition based on one or more signal quality measurements; and
means for returning to the first low power state after terminating
the cell acquisition.
14. The apparatus of claim 8, wherein the one or more signals
comprise at least one of a primary synchronization signal (PSS), a
secondary synchronization signal (SSS), or a physical broadcast
channel (PBCH).
15. An apparatus for wireless communication, comprising: at least
one processor configured to: exit a first low power state in order
to perform cell acquisition based on one or more signals
transmitted by a base station; and take one or more actions to
reduce acquisition time when performing the cell acquisition; and a
memory coupled to the at least one processor.
16. The apparatus of claim 15, wherein the at least one processor
is further configured to: receive an announcement with information
regarding opportunities when the one or more signals will be
transmitted with boosted transmission power; and take the one or
more actions by coordinating exiting the first low power state
based on the information in the announcement.
17. The apparatus of claim 16, wherein the at least one processor
is further configured to exit a second low power state to monitor
for one or more signals, based on cell acquisition already
performed during one of the announced opportunities.
18. The apparatus of claim 15, wherein the at least one processor
is configured to take the one or more actions by performing cell
acquisition while monitoring for a reduced set of synchronization
signals, wherein the reduced set is based at least in part on a
previously determined cell ID.
19. The apparatus of claim 18, wherein the at least one processor
is configured to monitor for the reduced set of synchronization
signals by searching for timing of a primary synchronization signal
(PSS) and secondary synchronization signal (SSS) corresponding to
the previously determined cell ID.
20. The apparatus of claim 15, wherein the at least one processor
is configured to take the one or more actions by: terminating the
cell acquisition based on one or more signal quality measurements;
and returning to the first low power state after terminating the
cell acquisition.
21. The apparatus of claim 15, wherein the one or more signals
comprise at least one of a primary synchronization signal (PSS), a
secondary synchronization signal (SSS), or a physical broadcast
channel (PBCH).
22. A computer-readable medium having computer executable code
stored thereon for: exiting a first low power state in order to
perform cell acquisition based on one or more signals transmitted
by a base station; and taking one or more actions to reduce
acquisition time when performing the cell acquisition.
23. The computer-readable medium of claim 22, further comprising
computer executable code stored thereon for receiving an
announcement with information regarding opportunities when the one
or more signals will be transmitted with boosted transmission
power, wherein taking the one or more actions comprises
coordinating exiting the first low power state based on the
information in the announcement.
24. The computer-readable medium of claim 23, further comprising
computer executable code stored thereon for exiting a second low
power state to monitor for one or more signals, based on cell
acquisition already performed during one of the announced
opportunities.
25. The computer-readable medium of claim 22, wherein taking the
one or more actions comprises performing cell acquisition while
monitoring for a reduced set of synchronization signals, wherein
the reduced set is based at least in part on a previously
determined cell ID.
26. The computer-readable medium of claim 25, wherein monitoring
for the reduced set of synchronization signals comprises searching
for timing of a primary synchronization signal (PSS) and secondary
synchronization signal (SSS) corresponding to the previously
determined cell ID.
27. The computer-readable medium of claim 22, wherein taking the
one or more actions comprises: terminating the cell acquisition
based on one or more signal quality measurements; and returning to
the first low power state after terminating the cell
acquisition.
28. The computer-readable medium of claim 22, wherein the one or
more signals comprise at least one of a primary synchronization
signal (PSS), a secondary synchronization signal (SSS), or a
physical broadcast channel (PBCH).
Description
CROSS-REFERENCE TO RELATED APPLICATION(S)
[0001] This application is a divisional application of U.S.
application Ser. No. 15/063,791, filed Mar. 8, 2016, which claims
the benefit of and priority to U.S. Provisional Application Ser.
No. 62/142,935, filed Apr. 3, 2015, both of which are assigned to
the assignee hereof and hereby expressly incorporated by reference
herein.
BACKGROUND
I. Field of the Disclosure
[0002] Certain aspects of the present disclosure generally relate
to wireless communications and, more particularly, to techniques
for reducing cell acquisition time by certain wireless devices,
such as machine type communication(s) (MTC) devices with coverage
enhancements.
II. Description of Related Art
[0003] Wireless communication systems are widely deployed to
provide various types of communication content such as voice, data,
and so on. These systems may be multiple-access systems capable of
supporting communication with multiple users by sharing the
available system resources (e.g., bandwidth and transmit power).
Examples of such multiple-access systems include code division
multiple access (CDMA) systems, time division multiple access
(TDMA) systems, frequency division multiple access (FDMA) systems,
3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE)
including LTE-Advanced systems and orthogonal frequency division
multiple access (OFDMA) systems.
[0004] Generally, a wireless multiple-access communication system
can simultaneously support communication for multiple wireless
terminals. Each terminal communicates with one or more base
stations via transmissions on the forward and reverse links. The
forward link (or downlink) refers to the communication link from
the base stations to the terminals, and the reverse link (or
uplink) refers to the communication link from the terminals to the
base stations. This communication link may be established via a
single-input single-output, multiple-input single-output or a
multiple-input multiple-output (MIMO) system.
[0005] A wireless communication network may include a number of
base stations that can support communication for a number of
wireless devices. Wireless devices may include user equipments
(UEs). Some UEs may be considered machine-type communication (MTC)
UEs, which may include remote devices, that may communicate with a
base station, another remote device, or some other entity. Machine
type communications (MTC) may refer to communication involving at
least one remote device on at least one end of the communication
and may include forms of data communication which involve one or
more entities that do not necessarily need human interaction. MTC
UEs may include UEs that are capable of MTC communications with MTC
servers and/or other MTC devices through Public Land Mobile
Networks (PLMN), for example.
SUMMARY
[0006] 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.
[0007] Certain aspects of the present disclosure provide techniques
and apparatus for reducing the amount of time associated with
searching and/or acquiring a cell.
[0008] Certain aspects of the present disclosure provide a method
for wireless communications by a base station (B S). The method
generally includes determining one or more opportunities for
assisting cell acquisition by one or more user equipments (UEs),
and boosting transmission power for one or more signals used for
cell acquisition during the determined opportunities.
[0009] Certain aspects of the present disclosure provide a method
for wireless communications by a user equipment (UE). The method
generally includes exiting a first low power state in order to
perform cell acquisition based on one or more signals transmitted
by a base station, and taking one or more actions to reduce
acquisition time when performing the cell acquisition.
[0010] Certain aspects of the present disclosure provide an
apparatus for wireless communications. The apparatus generally
includes means for determining one or more opportunities for
assisting cell acquisition by one or more UEs, and means for
boosting transmission power for one or more signals used for cell
acquisition during the determined opportunities.
[0011] Certain aspects of the present disclosure provide an
apparatus for wireless communications. The apparatus generally
includes means for exiting a first low power state in order to
perform cell acquisition based on one or more signals transmitted
by a base station, and means for taking one or more actions to
reduce acquisition time when performing the cell acquisition.
[0012] Certain aspects of the present disclosure provide an
apparatus for wireless communications. The apparatus generally
includes at least one processor configured to determine one or more
opportunities for assisting cell acquisition by one or more UEs,
and boost transmission power for one or more signals used for cell
acquisition during the determined one or more opportunities. The
apparatus also includes a memory coupled with the at least one
processor.
[0013] Certain aspects of the present disclosure provide an
apparatus for wireless communications. The apparatus generally
includes at least one processor configured to exit a first low
power state in order to perform cell acquisition based on one or
more signals transmitted by a base station, and take one or more
actions to reduce acquisition time when performing the cell
acquisition. The apparatus also includes a memory coupled with the
at least one processor.
[0014] Certain aspects of the present disclosure provide a
computer-readable medium having computer executable code stored
thereon. The computer-readable medium generally includes code for
determining one or more opportunities for assisting cell
acquisition by one or more UEs, and boosting transmission power for
one or more signals used for cell acquisition during the one or
more determined opportunities.
[0015] Certain aspects of the present disclosure provide a
computer-readable medium having computer executable code stored
thereon. The computer-readable medium generally includes code for
causing a UE to exit a first low power state in order to perform
cell acquisition based on one or more signals transmitted by a base
station, and taking one or more actions to reduce acquisition time
when performing the cell acquisition.
[0016] Numerous other aspects are provided including methods,
apparatus, systems, computer program products, and processing
systems. To the accomplishment of the foregoing and related ends,
the one or more aspects comprise the features hereinafter fully
described and particularly pointed out in the claims. The following
description and the annexed drawings set forth in detail certain
illustrative features of the one or more aspects. These features
are indicative, however, of but a few of the various ways in which
the principles of various aspects may be employed, and this
description is intended to include all such aspects and their
equivalents.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] 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. It is to be noted, however, that the appended drawings
illustrate only certain typical aspects of this disclosure and are
therefore not to be considered limiting of its scope, for the
description may admit to other equally effective aspects.
[0018] FIG. 1 is a block diagram conceptually illustrating an
example of a wireless communication network, in accordance with
certain aspects of the present disclosure.
[0019] FIG. 2 shows a block diagram conceptually illustrating an
example of a base station in communication with a user equipment
(UE) in a wireless communications network, in accordance with
certain aspects of the present disclosure.
[0020] FIG. 3 is a block diagram conceptually illustrating an
example of a frame structure in a wireless communications network,
in accordance with certain aspects of the present disclosure.
[0021] FIG. 4 is a block diagram conceptually illustrating two
exemplary subframe formats with the normal cyclic prefix, in
accordance with certain aspects of the present disclosure.
[0022] FIG. 5 illustrates example signals that may be used in a
cell search procedure, in accordance with certain aspects of the
present disclosure.
[0023] FIG. 6 illustrates example operations for wireless
communications that may be performed by a base station, in
accordance with certain aspects of the present disclosure.
[0024] FIG. 7 illustrates example operations for wireless
communications that may be performed by a user equipment, in
accordance with certain aspects of the present disclosure.
[0025] FIG. 8 illustrates an example scenario in which a BS may
boost the transmission power of one or more signals used for cell
acquisition, in accordance with certain aspects of the present
disclosure.
[0026] FIG. 9 illustrates an example scenario in which a BS may
boost the transmission power of one or more signals used for cell
acquisition, in accordance with certain aspects of the present
disclosure.
[0027] FIG. 10 illustrates an example scenario in which a UE may
terminate cell acquisition based on one or more signal quality
measurements, in accordance with certain aspects of the present
disclosure.
[0028] 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 embodiment may be beneficially utilized on other
embodiments without specific recitation.
DETAILED DESCRIPTION
[0029] Aspects of the present disclosure provide various enhanced
techniques that may be used to reduce the time associated with
searching and acquiring a cell, relative to traditional cell
acquisition techniques. The techniques may used by certain devices,
such as MTC devices and/or enhanced or evolved MTC (eMTC) devices,
to reduce the amount of time associated with receiving one or more
signals (e.g., such as primary synchronization signal, secondary
synchronization signal, physical broadcast channel, etc.) used for
cell acquisition.
[0030] For example, as described in more detail below, in some
aspects, a base station may assist one or more user equipments in
cell acquisition by boosting the transmission power of the one or
more signals. These signals may be boosted during certain
opportunities that are based, in part, on one or more power states
of the user equipments. Similarly, in some aspects, as also
described in more detail below, user equipments may take one or
more actions to reduce acquisition time when performing the cell
acquisition. Such actions may include exiting one or more low power
states to monitor for the one or more signals that are power
boosted from the base station, monitoring for a reduced set of the
one or more signals, terminating the cell acquisition based on
signal quality measurements, etc.
[0031] The techniques described herein may be used for various
wireless communication networks such as CDMA, TDMA, FDMA, OFDMA,
SC-FDMA and other networks. The terms "network" and "system" are
often used interchangeably. A CDMA network may implement a radio
technology such as universal terrestrial radio access (UTRA),
cdma2000, etc. UTRA includes wideband CDMA (WCDMA), time division
synchronous CDMA (TD-SCDMA), and other variants of CDMA. cdma2000
covers IS-2000, IS-95 and IS-856 standards. A TDMA network may
implement a radio technology such as global system for mobile
communications (GSM). An OFDMA network may implement a radio
technology 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), in both frequency division duplex (FDD) and
time division duplex (TDD), are new 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 radio technologies mentioned above as well as
other wireless networks and radio technologies. For clarity,
certain aspects of the techniques are described below for
LTE/LTE-Advanced, and LTE/LTE-Advanced terminology is used in much
of the description below. LTE and LTE-A are referred to generally
as LTE.
[0032] FIG. 1 illustrates an example wireless communication network
100, in which aspects of the present disclosure may be practiced.
For example, one or more signals used for searching for a cell
and/or acquiring a cell may be transmitted by one or more BSs/eNBs
110 in the wireless communication network 100 to one or more UEs
120 in the wireless communication network 100. As will be described
in more detail below, the techniques presented herein may be used
by the eNBs 110 and/or UE(s) 120 to reduce the amount of time
associated with UEs 120 performing cell acquisition based on the
one or more signals. As used herein, the term "cell acquisition"
may be used to refer to searching for a cell and/or acquiring the
cell (e.g., synchronizing to the cell).
[0033] The wireless communication network 100 may be an LTE network
or some other wireless network. Wireless communication network 100
may include a number of evolved Node Bs (eNBs) 110 and other
network entities. An eNB is an entity that communicates with user
equipments (UEs) and may also be referred to as a base station, a
Node B, an access point (AP), etc. Each eNB may provide
communication coverage for a particular geographic area. In 3GPP,
the term "cell" can refer to a coverage area of an eNB and/or an
eNB subsystem serving this coverage area, depending on the context
in which the term is used.
[0034] An eNB may provide communication coverage for a macro cell,
a pico cell, a femto cell, and/or other types of cell. A macro cell
may cover a relatively large geographic area (e.g., several
kilometers in radius) and may allow unrestricted access by UEs with
service subscription. A pico cell may cover a relatively small
geographic area and may allow unrestricted access by UEs with
service subscription. A femto cell may cover a relatively small
geographic area (e.g., a home) and may allow restricted access by
UEs having association with the femto cell (e.g., UEs in a closed
subscriber group (CSG)). An eNB for a macro cell may be referred to
as a macro eNB. An eNB for a pico cell may be referred to as a pico
eNB. An eNB for a femto cell may be referred to as a femto eNB or a
home eNB (HeNB). In the example shown in FIG. 1, an eNB 110a may be
a macro eNB for a macro cell 102a, an eNB 110b may be a pico eNB
for a pico cell 102b, and an eNB 110c may be a femto eNB for a
femto cell 102c. An eNB may support one or multiple (e.g., three)
cells. The terms "eNB", "base station," and "cell" may be used
interchangeably herein.
[0035] Wireless communication network 100 may also include relay
stations. A relay station is an entity that can receive a
transmission of data from an upstream station (e.g., an eNB or a
UE) and send a transmission of the data to a downstream station
(e.g., a UE or an eNB). A relay station may also be a UE that can
relay transmissions for other UEs. In the example shown in FIG. 1,
a relay (station) eNB 110d may communicate with macro eNB 110a and
a UE 120d in order to facilitate communication between eNB 110a and
UE 120d. A relay station may also be referred to as a relay eNB, a
relay base station, a relay, etc.
[0036] Wireless communication network 100 may be a heterogeneous
network that includes eNBs of different types, e.g., macro eNBs,
pico eNBs, femto eNBs, relay eNBs, etc. These different types of
eNBs may have different transmit power levels, different coverage
areas, and different impact on interference in wireless
communication network 100. For example, macro eNBs may have a high
transmit power level (e.g., 5 to 40 W) whereas pico eNBs, femto
eNBs, and relay eNBs may have lower transmit power levels (e.g.,
0.1 to 2 W).
[0037] A network controller 130 may couple to a set of eNBs and may
provide coordination and control for these eNBs. Network controller
130 may communicate with the eNBs via a backhaul. The eNBs may also
communicate with one another, e.g., directly or indirectly via a
wireless or wireline backhaul.
[0038] UEs 120 (e.g., 120a, 120b, 120c) may be dispersed throughout
wireless communication network 100, and each UE may be stationary
or mobile. A UE may also be referred to as an access terminal, a
terminal, a mobile station (MS), a subscriber unit, a station
(STA), etc. Examples of UEs may include a cellular 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
smart phone, a netbook, a smartbook, an ultrabook, gaming devices,
navigation devices, virtual reality devices, wearable devices
(e.g., smart glasses/goggles/heads-up displays, smart watch, smart
wristband, smart clothing), drones, robots/robotic devices,
vehicular devices, etc. Some UEs may be MTC UEs. Examples of MTC
UEs include sensors, meters, monitors, location tags, drones,
trackers, robots/robotic devices, etc. To enhance coverage of
certain devices, such as MTC devices, "bundling" may be utilized in
which certain transmissions are sent as a bundle of transmissions,
for example, with the same information transmitted over multiple
subframes. Some MTC UEs, as well as other UEs, may be implemented
as internet of things (IoT) devices (e.g., narrowband IoT (NB-IoT)
devices) or internet of everything (IoE) devices. In FIG. 1, a
solid line with double arrows indicates desired transmissions
between a UE and a serving eNB, which is an eNB designated to serve
the UE on the downlink and/or uplink. A dashed line with double
arrows indicates potentially interfering transmissions between a UE
and an eNB.
[0039] One or more UEs 120 in the wireless communication network
100 (e.g., an LTE network) may also be low cost, low data rate
devices, e.g., such as low cost MTC UEs, low cost eMTC UEs, low
cost IoT UEs, etc. The low cost UEs may co-exist with legacy and/or
advanced UEs in the LTE network and may have one or more
capabilities that are limited when compared to the other UEs (e.g.,
non-low cost UEs) in the wireless network. For example, in LTE
Rel-12, when compared to legacy and/or advanced UEs in the LTE
network, the low cost UEs may operate with one or more of the
following: a reduction in maximum bandwidth (relative to legacy
UEs), a single receive radio frequency (RF) chain, reduction of
peak rate (e.g., a maximum of 1000 bits for a transport block size
(TB S) may be supported), reduction of transmit power, rank 1
transmission, half duplex operation, etc. In some cases, if half
duplex operation is supported, the low cost UEs may have a relaxed
switching timing from transmit to receive (or from receive to
transmit) operations. For example, in one case, compared to a
switching timing of 20 microseconds (us) for legacy and/or advanced
UEs, the low cost UEs may have a relaxed switching timing of 1
millisecond (ms).
[0040] In some cases, the low cost UEs may also be able to monitor
downlink (DL) control channels in the same away as legacy and/or
advanced UEs in the LTE network monitor DL control channels. For
example, the low cost UEs may monitor for wideband control channels
in the first few symbols (e.g., physical downlink control channel
(PDCCH)) as well as narrowband control channels occupying a
relatively narrowband, but spanning a length of a subframe (e.g.,
enhanced PDCCH (ePDCCH)).
[0041] The wireless communication network 100, as an alternative or
in addition to supporting MTC operation, may support additional MTC
enhancements (e.g., eMTC operations). For example, low cost eMTC
UEs (e.g., in LTE Rel-13) may be able to support narrowband
operation (e.g., operating on one or more narrowband regions
partitioned out of an available system bandwidth that is supported
by a particular RAT. Referring to LTE, low cost UEs may operate on
a particular narrowband assignment of 1.4 MHz or six resource
blocks (RBs) (partitioned out of the available system bandwidth)
while co-existing within a wider system bandwidth (e.g., at
1.4/3/5/10/15/20 MHz). The low cost eMTC UEs may also support one
or more coverage modes of operation (where repetitions of the same
message may be bundled or transmitted across multiple subframes).
For example, the low cost eMTC UE may support coverage enhancements
up to 15 dB with respect to legacy LTE users.
[0042] As used herein, devices with limited communication
resources, such as MTC devices, eMTC devices, etc. are referred to
generally as low cost UEs. Similarly, legacy devices, such as
legacy and/or advanced UEs (e.g., in LTE) are referred to generally
as non-low cost UEs.
[0043] In some cases, a UE (e.g., low cost UE or non-low cost UE)
may perform a cell search and acquisition procedure before
communicating in the network. In one case, with reference to the
LTE network illustrated in FIG. 1 as an example, a UE may perform a
cell search and acquisition procedure when the UE is not connected
to a LTE cell and wants to access the LTE network. In these cases,
the UE may have just powered on, restored a connection after
temporarily losing connection to the LTE cell, etc.
[0044] In other cases, a UE may perform the cell search and
acquisition procedure when the UE is already connected to a LTE
cell. For example, the UE may have detected a new LTE cell and may
prepare a handover to the new cell. As another example, the UE may
be operating in one or more low power states (e.g., may support
discontinuous reception (DRX)) and, upon exiting the one or more
low power states, may perform the cell search and acquisition
procedure (even though the UE is still in connected mode).
[0045] FIG. 2 is a block diagram of a design of BS/eNB 110 and UE
120, which may be one of the BSs/eNBs 110 and one of the UEs 120,
respectively, in FIG. 1. BS 110 may be equipped with T antennas
234a through 234t, and UE 120 may be equipped with R antennas 252a
through 252r, where in general T>1 and R 1.
[0046] At BS 110, a transmit processor 220 may receive data from a
data source 212 for one or more UEs, select one or more modulation
and coding schemes (MCSs) for each UE based on channel quality
indicators (CQIs) received from the UE, process (e.g., encode and
modulate) the data for each UE based on the MCS(s) selected for the
UE, and provide data symbols for all UEs. Transmit processor 220
may also process system information (e.g., for semi-static resource
partitioning information (SRPI), etc.) and control information
(e.g., CQI requests, grants, upper layer signaling, etc.) and
provide overhead symbols and control symbols. Processor 220 may
also generate reference symbols for reference signals (e.g., the
common reference signal (CRS)) and synchronization signals (e.g.,
the primary synchronization signal (PSS) and secondary
synchronization signal (SSS)). A transmit (TX) multiple-input
multiple-output (MIMO) processor 230 may perform spatial processing
(e.g., precoding) on the data symbols, the control symbols, the
overhead symbols, and/or the reference symbols, if applicable, and
may provide T output symbol streams to T modulators (MODs) 232a
through 232t. Each MOD 232 may process a respective output symbol
stream (e.g., for OFDM, etc.) to obtain an output sample stream.
Each MOD 232 may further process (e.g., convert to analog, amplify,
filter, and upconvert) the output sample stream to obtain a
downlink signal. T downlink signals from modulators 232a through
232t may be transmitted via T antennas 234a through 234t,
respectively.
[0047] At UE 120, antennas 252a through 252r may receive the
downlink signals from BS 110 and/or other BSs and may provide
received signals to demodulators (DEMODs) 254a through 254r,
respectively. Each DEMOD 254 may condition (e.g., filter, amplify,
downconvert, and digitize) its received signal to obtain input
samples. Each DEMOD 254 may further process the input samples
(e.g., for OFDM, etc.) to obtain received symbols. A MIMO detector
256 may obtain received symbols from all R demodulators 254a
through 254r, perform MIMO detection on the received symbols if
applicable, and provide detected symbols. A receive processor 258
may process (e.g., demodulate and decode) the detected symbols,
provide decoded data for UE 120 to a data sink 260, and provide
decoded control information and system information to a
controller/processor 280. A channel processor may determine
reference signal received power (RSRP), received signal strength
indicator (RSSI), reference signal received quality (RSRQ), CQI,
etc.
[0048] On the uplink, at UE 120, a transmit processor 264 may
receive and process data from a data source 262 and control
information (e.g., for reports comprising RSRP, RSSI, RSRQ, CQI,
etc.) from controller/processor 280. Processor 264 may also
generate reference symbols for one or more reference signals. The
symbols from transmit processor 264 may be precoded by a TX MIMO
processor 266 if applicable, further processed by MODs 254a through
254r (e.g., for SC-FDM, OFDM, etc.), and transmitted to BS 110. At
BS 110, the uplink signals from UE 120 and other UEs may be
received by antennas 234, processed by DEMODs 232, detected by a
MIMO detector 236 if applicable, and further processed by a receive
processor 238 to obtain decoded data and control information sent
by UE 120. Processor 238 may provide the decoded data to a data
sink 239 and the decoded control information to
controller/processor 240. BS 110 may include communication unit 244
and communicate to network controller 130 via communication unit
244. Network controller 130 may include communication unit 294,
controller/processor 290, and memory 292.
[0049] Controllers/processors 240 and 280 may direct the operation
at BS 110 and UE 120, respectively. For example,
controller/processor 240 and/or other processors and modules at BS
110 may perform or direct operations 600 illustrated in FIG. 6
and/or other processes for the techniques described herein.
Similarly, controller/processor 280 and/or other processors and
modules at UE 120 may perform or direct operations 700 illustrated
in FIG. 7 and/or other processes for the techniques described
herein. Memories 242 and 282 may store data and program codes for
BS 110 and UE 120, respectively. A scheduler 246 may schedule UEs
for data transmission on the downlink and/or uplink.
[0050] FIG. 3 shows an exemplary frame structure 300 for FDD in
LTE. The transmission timeline for each of the downlink and uplink
may be partitioned into units of radio frames. Each radio frame may
have a predetermined duration (e.g., 10 ms)) and may be partitioned
into 10 subframes with indices of 0 through 9. Each subframe may
include two slots. Each radio frame may thus include 20 slots with
indices of 0 through 19. Each slot may include L symbol periods,
e.g., seven symbol periods for a normal cyclic prefix (as shown in
FIG. 3) or six symbol periods for an extended cyclic prefix. The 2L
symbol periods in each subframe may be assigned indices of 0
through 2L-1.
[0051] In LTE, an eNB may transmit a primary synchronization signal
(PSS) and a secondary synchronization signal (SSS) on the downlink
in the center 1.08 MHz of the system bandwidth for each cell
supported by the eNB. The PSS and SSS may be transmitted in symbol
periods 6 and 5, respectively, in subframes 0 and 5 of each radio
frame with the normal cyclic prefix, as shown in FIG. 3. The PSS
and SSS may be used by UEs for cell search and acquisition. For
example, the PSS may provide the UE with information regarding the
physical layer identity (e.g., 0 to 2), which may identify which of
three groups of physical layer cell identifies a LTE cell may
belong. The PSS may also be used by the UE in symbol timing
detection, frequency offset detection, etc. The SSS may provide the
UE with information regarding the physical layer cell identity
group number (e.g., 0 to 167) and may be used by the UE for radio
frame timing detection, cyclic prefix length detection, time
division duplexing (TDD)/frequency division duplexing (FDD)
detection, etc.
[0052] The UE may determine the physical layer cell identity (PCI)
for a given cell based on the physical layer identity (e.g., from
PSS) and the physical layer cell identity group number (e.g., from
SSS). For example, in one embodiment, the PCI may be equal to
3.times.(physical layer cell identity group)+physical layer
identity. Once the UE determines the PCI for a given cell, as
described below, the UE may determine the location of reference
signals transmitted from the cell and may be able to receive and
decode system information (e.g., used for acquiring the cell)
transmitted from the cell.
[0053] The eNB may transmit a cell-specific reference signal (CRS)
across the system bandwidth for each cell supported by the eNB. The
CRS may be transmitted in certain symbol periods of each subframe
and may be used by the UEs to perform channel estimation, channel
quality measurement, and/or other functions. The eNB may also
transmit a physical broadcast channel (PBCH) in symbol periods 0 to
3 in slot 1 of certain radio frames.
[0054] The PBCH may carry some system information (e.g., the master
information block (MIB)) that, in general, may be used by UEs for
initial access to the cell, and the like. For example, the PBCH may
carry information regarding system bandwidth, number of transmit
antennas, system frame number, etc. The eNB may also transmit other
system information such as system information blocks (SIBs) on a
physical downlink shared channel (PDSCH) in certain subframes. The
eNB may transmit control information/data on a physical downlink
control channel (PDCCH) in the first B symbol periods of a
subframe, where B may be configurable for each subframe. The eNB
may transmit traffic data and/or other data on the PDSCH in the
remaining symbol periods of each subframe.
[0055] The PSS, SSS, CRS, and PBCH in LTE are described in 3GPP TS
36.211, entitled "Evolved Universal Terrestrial Radio Access
(E-UTRA); Physical Channels and Modulation," which is publicly
available.
[0056] FIG. 4 shows two example subframe formats 410 and 420 for
the downlink with a normal cyclic prefix. The available time
frequency resources for the downlink may be partitioned into
resource blocks. Each resource block may cover 12 subcarriers in
one slot and may include a number of resource elements. Each
resource element 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.
[0057] Subframe format 410 may be used for an eNB equipped with two
antennas. A CRS may be transmitted from antennas 0 and 1 in symbol
periods 0, 4, 7, and 11. A reference signal is a signal that is
known a priori by a transmitter and a receiver and may also be
referred to as pilot. A CRS is a reference signal that is specific
for a cell, e.g., generated based on a cell identity (ID). In FIG.
4, for a given resource element with label Ra, a modulation symbol
may be transmitted on that resource element from antenna a, and no
modulation symbols may be transmitted on that resource element from
other antennas. Subframe format 420 may be used for an eNB equipped
with four antennas. A CRS may be transmitted from antennas 0 and 1
in symbol periods 0, 4, 7, and 11 and from antennas 2 and 3 in
symbol periods 1 and 8. For both subframe formats 410 and 420, a
CRS may be transmitted on evenly spaced subcarriers, which may be
determined based on cell ID. Different eNBs may transmit their CRSs
on the same or different subcarriers, depending on their cell IDs.
For both subframe formats 410 and 420, resource elements not used
for the CRS may be used to transmit data (e.g., traffic data,
control data, and/or other data).
[0058] An interlace structure may be used for each of the downlink
and uplink for FDD in LTE. For example, Q interlaces with indices
of 0 through Q-1 may be defined, where Q may be equal to 4, 6, 8,
10, or some other value. Each interlace may include subframes that
are spaced apart by Q frames. In particular, interlace q may
include subframes q, q+Q, q+2Q, etc., where q.di-elect cons.{0, . .
. , Q-1}.
[0059] The wireless network may support hybrid automatic
retransmission request (HARQ) for data transmission on the downlink
and uplink. For HARQ, a transmitter (e.g., an eNB) may send one or
more transmissions of a packet until the packet is decoded
correctly by a receiver (e.g., a UE) or some other termination
condition is encountered. For synchronous HARQ, all transmissions
of the packet may be sent in subframes of a single interlace. For
asynchronous HARQ, each transmission of the packet may be sent in
any subframe.
[0060] A UE may be located within the coverage of multiple eNBs.
One of these eNBs may be selected to serve the UE. The serving eNB
may be selected based on various criteria such as received signal
strength, received signal quality, pathloss, etc. Received signal
quality may be quantified by a signal-to-noise-and-interference
ratio (SINR), or a reference signal received quality (RSRQ), or
some other metric. The UE may operate in a dominant interference
scenario in which the UE may observe high interference from one or
more interfering eNBs.
[0061] As mentioned above, one or more UEs in the wireless
communication network (e.g., wireless communication network 100)
may be devices that have limited communication resources, such as
low cost UEs, as compared to other (non-low cost) devices in the
wireless communication network. For example, as noted above, The
low cost UE may be a link budget limited device and may operate in
different modes of operation (e.g. using different numbers of
repetitions for messages transmitted to or from the low cost UE)
based on its link budget limitation. For example, in some cases,
the low cost UE may operate in a normal coverage mode in which
there is little to no repetition (e.g., the amount of repetition
needed for the UE to successfully receive and/or transmit a message
may be low or repetition may not even be needed). Alternatively, in
some cases, the low cost UE may operate in a coverage enhancement
(CE) mode in which there may be high amounts of repetition.
Further, in some cases, non-low cost UEs may also be able to
support the CE mode.
[0062] In some cases, when operating in CE mode, a UE (e.g., low
cost UE and/or non-low cost UE) may perform a cell search and
acquisition procedure (e.g., upon powering up, exiting a low power
mode(s), entering a new cell, handover, etc.). FIG. 5 illustrates
an example cell search procedure 500 that may be used by certain
devices operating in CE mode.
[0063] As shown in FIG. 5, at 502, the UE may first detect PSS
transmitted from a BS. At 504, the UE may then detect SSS
transmitted from the BS. In some cases, as shown, even when the UE
is in CE mode, the PSS and SSS may not be transmitted with
repetition. However, in other cases, the PSS and SSS may be
transmitted with repetition. As noted above, upon detecting the PSS
and SSS, the UE may determine PCI for a given cell and may be able
to receive system information broadcasted (e.g., in a PBCH) from
the cell.
[0064] At 506, the UE may receive (with repetition) a PBCH
broadcasted from a BS. In some cases, the UE may be able to receive
the PBCH with one or more additional repetitions of the PBCH across
multiple subframes (e.g., such that UEs in bad radio channel
conditions are able to successfully receive and/or decode the PBCH
transmitted in the cell). The repetition of PBCH may be within
subframe 0 and additionally in other subframes (e.g., subframe 5,
etc.).
[0065] As mentioned above, in some cases (e.g., when a UE supports
DRX operation), a UE operating in a low power state may perform a
cell search and acquisition procedure upon exiting (or waking up
from) the low power state. For example, upon waking up from the low
power state, the UE may have an inaccurate timing synchronization
(e.g., due, in part, to a local clock drifting), the UE's local
oscillator may have drifted, etc. Thus, in some cases, even when a
UE is in connected mode, but in DRX operation, the UE may perform a
cell search and acquisition procedure to correct timing and/or
frequency synchronization to a cell.
[0066] However, for certain devices that have limited communication
resources, such as low cost UEs, the cell search and acquisition
procedure may take an excessive amount of time. For example, low
cost UEs may, in general, operate in environments with very poor
radio channel conditions as measured by one or metrics such as
signal-to-noise ratio (SNR), pathloss, received signal strength,
and the like. In one case, as an example, a UE may operate with a
SNR of -15 dB while in CE mode. When operating in poor radio
channel conditions, the low cost UEs may use a number of
repetitions (e.g., CE mode) of one or more cell acquisition signals
(e.g., PSS, SSS, PBCH, etc.) before the UE is able to acquire the
cell. In these circumstances, the UE may miss paging opportunities
(e.g., if the search is not successful) and/or increase battery
consumption (due, in part, to the increased time it takes to
perform cell acquisition as the UE may have to wake up ahead of
time to search for the cell).
[0067] Accordingly, it may be helpful to provide techniques that
may reduce the time associated with performing cell
acquisition.
Techniques for Enhancing Cell Acquisition
[0068] As mentioned above, one or more techniques presented herein
may be used by one or more BSs to assist certain devices (e.g., low
cost UEs, non-low cost UEs) in performing cell acquisition. The one
or more techniques presented herein may also be used by certain
devices (e.g., low cost UEs, non-low cost UEs) to reduce the time
associated with performing cell acquisition. As used herein, the
term "cell acquisition" may be used to refer to searching for a
cell and/or acquiring the cell (e.g., synchronizing to the
cell).
[0069] FIG. 6 illustrates example operations 600 for wireless
communications, in accordance with certain aspects of the present
disclosure. The operations 600 can performed by a BS, such as one
of the BSs/eNBs 110 illustrated in FIGS. 1 and 2.
[0070] The operations 600 may begin, at 602, where the BS
determines one or more opportunities for assisting cell acquisition
by one or more UEs. At 604, the BS boosts transmission power for
one or more signals used for cell acquisition during the determined
one or more opportunities.
[0071] FIG. 7 illustrates example operations 700 for wireless
communications, in accordance with certain aspects of the present
disclosure. The operations 700 can be performed by a UE, such as a
low cost UE, non-low cost UE, etc., which may be one of the UEs 120
illustrated in FIGS. 1 and 2.
[0072] The operations 700 may begin, at 702, where the UE exits a
first low power state in order to perform cell acquisition based on
one or more signals transmitted by a BS. At 704, the UE takes one
or more actions to reduce acquisition time when performing the cell
acquisition. In some aspects, taking one or more actions may
include performing cell acquisition while monitoring for a reduced
set of the one or more signals transmitted by the BS. As described
in more detail below with reference to FIGS. 8 and 9, in some
aspects, taking one or more actions may include coordinating
exiting a low power state based on information (e.g., an
announcement) regarding the determined opportunities. As described
in more detail below with reference to FIG. 10, in some aspects,
taking one or more actions may include terminating the cell
acquisition based on one or more signal quality measurements and
returning to a low power state after terminating the cell
acquisition.
[0073] According to certain aspects, the BS may assist UEs in
performing cell acquisition by boosting (during the determined
opportunities) transmission power of one or more signals (e.g.,
PSS, SSS, PBCH, etc.) used by the UEs when performing cell
acquisition.
[0074] For example, according to an aspect, the BS may be able to
boost transmission power of the one or more signals by allocating
all available transmission power to a center bandwidth region of
available system bandwidth. In some cases, the center bandwidth
region may be 6 resource blocks (RBs) or 1.4 MHz. In some cases,
the center bandwidth region may be a center narrowband region
(e.g., of 6 RBs, etc.) partitioned out of a wider system bandwidth
(e.g., at 1.4/3/5/10/15/20 MHz). In some cases, the BS may boost
the transmission power of the one or more signals by allocating all
available transmission power to another narrowband region (e.g., as
opposed to the center narrowband region) partitioned out the wider
system bandwidth.
[0075] Alternatively or additionally, according to certain aspects,
the BS may reduce a number of physical downlink shared channel
(PDSCH) assignments, during the determined opportunities, in order
to boost the transmission power of the one or more signals used for
cell acquisition. In certain aspects, the BS may determine to
transmit zero or a reduced number of PDSCH assignments, during the
determined opportunities, in order to boost the transmission power
of the one or more signals used for cell acquisition. In some
aspects, the UE may still transmit CRS in the whole system
bandwidth while boosting the transmission power of the one or more
signals (e.g., by allocating all transmission power to a particular
narrowband region).
[0076] According to certain aspects, the BS may determine
opportunities in which to boost transmission power based on
knowledge of when one or more UEs are expected to exit a low power
state. For example, the BS may have knowledge of the DRX
configuration and/or paging cycle of one or more UEs operating in
the wireless communication network, and may use the knowledge of
the DRX configuration and/or paging cycle to determine the awake
cycles of the one or more UEs.
[0077] FIG. 8, for example, illustrates an example scenario in
which a BS (e.g., BS/eNB 110) may boost the transmission power of
one or more signals (e.g., to UE 120) used for cell acquisition
during one or more determined opportunities, according to certain
aspects of the present disclosure.
[0078] As shown in FIG. 8, the BS may determine (e.g., based on a
DRX configuration and/or paging cycle of the UE) that the UE 120 is
expected to be awake at 802 and 806 (e.g., after exiting a low
power state at 804). Based on this knowledge, the BS may determine
to boost the transmission power of the one or more signals (e.g.,
relative to the transmission power of the one or more signals
subsequently transmitted at 810) during a time (e.g., boosting
opportunities 808 and 812) when the UE is expected to be listening
for the one or more signals. According to certain aspects, as
shown, the boosting opportunities 808 and 812 may partially overlap
the awake cycle of the UE. According to certain aspects, although
not shown, the boosting opportunities may completely overlap the
awake cycle of the UE. Further, although one UE is shown in FIG. 8,
the BS may also have knowledge of the DRX configuration of multiple
UEs and may determine the boosting opportunities based on the DRX
configuration of multiple UEs.
[0079] According to certain aspects, the BS may also be able to
configure the DRX configurations of one or more UEs in an effort to
align awake cycles of the one or more UEs. For example, in some
cases, if there are several UEs with awake cycles that do not
overlap, the BS may attempt to align some (or all) of the awake
cycles of the UEs in order to reduce the amount of power boosting
opportunities.
[0080] Additionally or alternatively, according to certain aspects,
the BS may announce information regarding the boosting
opportunities to the one or more UEs. For example, the BS may
periodically or aperiodically boost the transmission power of the
one or more signals to the UEs and announce the periodic (or
aperiodic) boosting opportunities to the UEs. The UE may then
decide whether or not it will awake to receive the one or more
signals during the announced boosting opportunities.
[0081] FIG. 9, for example, illustrates an example scenario in
which a BS (e.g., BS 110) may boost the transmission power of one
or more signals (e.g., to UE 120) used for cell acquisition during
an announced boosting opportunity, according to certain aspects of
the present disclosure.
[0082] According to certain aspects, a UE may receive an
announcement from the BS with information regarding opportunities
when the one or more signals will be transmitted with boosted
transmission power. For example, in some cases, the BS may announce
the information regarding the boosting opportunities to the one or
more UEs via a broadcast of system information. After receiving the
announcement information, the UE may coordinate exiting the first
low power state based on the information in the announcement.
[0083] According to certain aspects, a UE may initially be in a
first low power state 902 (e.g., sleep mode), but may decide to
coordinate exiting the first low power state 902 based on the
information in the announcement. For example, as shown in FIG. 9, a
UE may determine to wake up ahead of time at 904 (e.g. by exiting
the first low power state 902) in order to use (e.g., monitoring
for the cell acquisition signals during) the announced power boost
at 910, based on knowledge of the boosting opportunities. Note the
boosted transmission power of the cell acquisition signals (e.g.,
PSS, SSS, PBCH, etc.) transmitted at 910 is relative to the
transmission power of the cell acquisition signals transmitted at
912 and 914.
[0084] According to certain aspects, the UE may exit a second lower
power state (different from the first low power state) to monitor
for one or more signals (e.g., paging messages, etc.), based on the
cell acquisition already performed during one of the announced
opportunities. For example, after receiving the one or more cell
acquisition signals during the boosted opportunity 904, the UE may
then decide to enter a second low power state 906 (e.g., light
sleep mode) until it is time for the UE to awake at 908 (e.g.,
based on its original awake cycle). The UE may exit the second low
power state 906 to monitor for one or more signals (e.g., paging
messages, etc.) not associated with the one or more signals
obtained during the announced opportunity. In certain aspects,
while in the second low power state 906, the UE may have limited
amount of RF monitoring (e.g., to prevent drifting of its local
oscillator) while turning off some processing (e.g., turn off its
digital signal processor (DSP) receiver) in order to reduce power
consumption.
[0085] As mentioned above, in some cases, when a UE accesses a cell
for the first time, the UE may not know the strongest cell and
therefore may perform a cell search and acquisition procedure to
acquire the cell. However, as noted above, every time the cell
acquisition is performed, the UE may have to detect several amounts
of information, such as cell ID (PCI), symbol timing information,
frame timing information (e.g., SF0/5), cyclic prefix length (e.g.,
whether normal or extended cyclic prefix is used), whether TDD/FDD
is utilized, etc. Searching for such a large number of hypotheses
may increase the amount of time associated with the cell
acquisition procedure.
[0086] Accordingly, it may be helpful to provide techniques that
allow a UE to reduce the time associated with searching for
synchronization signals.
[0087] According to certain aspects, the techniques presented
herein may reduce the time associated with performing cell
acquisition by allowing UEs to monitor for a reduced set of
synchronization signals when performing cell acquisition. For
example, according to certain aspects, the reduced set may be
based, at least in part, on a previously determined cell ID,
normal/long cyclic prefix, or TDD/FDD information, etc.
[0088] For certain devices (e.g., for low cost UEs) exiting a low
power state (e.g., the first power state), the low cost UE may be
able to determine with high probability that some of the
information previously determined from the synchronization signals
is the same. For example, for low cost UEs that, in general, have
low mobility, the low cost UE may be able to determine that the
strongest cell ID is the same as the cell ID of the cell that the
low cost UE was synchronized to before entering the low power
state. Similarly, the low cost UE may be able to determine that the
TDD/FDD information, cyclic prefix length information, etc. are
also the same.
[0089] Thus, according to certain aspects, upon exiting the first
low power state, a UE may be able to reduce the number of possible
hypothesis that have to be searched by monitoring only for a timing
of a PSS and SSS corresponding to the previously determined cell ID
(e.g., as opposed to monitoring for a cell ID, cyclic prefix
length, TDD/FDD determination associated with PSS and SSS in
addition to the timing of a PSS and SSS).
[0090] As also mentioned above, certain devices (e.g., low cost
UEs) may operate in poor radio channel conditions, which may
increase the time needed for the UEs to successfully perform cell
acquisition when waking up (e.g., since the operating channel
conditions may be too poor to receive the cell acquisition
signals).
[0091] Accordingly, it may be helpful to provide techniques that
allow the UE temporarily cease the cell acquisition procedure when
operating in poor radio channel conditions.
[0092] According to certain aspects, the techniques presented
herein may allow the UE to terminate cell acquisition based on one
or more signal quality measurements and return to the first low
power state after terminating the cell acquisition.
[0093] FIG. 10, for example, illustrates an example scenario in
which a UE 120 may terminate cell acquisition based on one or more
signal quality measurements, according to certain aspects of the
present disclosure.
[0094] As shown in FIG. 10, if a UE determines, upon exiting the
first low power state at 1002 to perform cell acquisition, that
radio channel conditions are poor, the UE may decide to stop
searching for synchronization signals (e.g., PSS, SSS, PBCH, etc.)
and return to the first low power state at 1004 after terminating
the cell acquisition. As also shown, upon waking up at 1006 (e.g.,
during its next awake cycle), the UE may continue the cell
acquisition procedure after determining that the radio channel
conditions are good.
[0095] The one or more signal quality measurements may be a
received signal strength indicator (RSSI) measurement, RSRP,
pathloss measurement, SNR, or some other metric. In some aspects,
this technique may provide time diversity, reduce power
consumption, etc.
[0096] The various techniques presented herein may improve the time
associated with performing cell acquisition and, as a result,
improve device performance and/or reduce power consumption.
[0097] 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).
[0098] As used herein, the term "determining" encompasses a wide
variety of actions. For example, "determining" may include
calculating, deciding, detecting, computing, processing, deriving,
investigating, looking up (e.g., looking up in a table, a database
or another data structure), ascertaining and the like. Also,
"determining" may include receiving (e.g., receiving information),
accessing (e.g., accessing data in a memory) and the like. Also,
"determining" may include resolving, selecting, choosing,
establishing and the like.
[0099] In some cases, rather than actually communicating a frame, a
device may have an interface to communicate a frame for
transmission or reception. For example, a processor may output or
transmit a frame, via a bus interface, to an RF front end for
transmission. Similarly, rather than actually receiving a frame, a
device may have an interface to obtain a frame received from
another device. For example, a processor may obtain (or receive) a
frame, via a bus interface, from an RF front end for
transmission.
[0100] The methods disclosed herein comprise one or more steps or
actions for achieving the described method. The method steps and/or
actions may be interchanged with one another without departing from
the scope of the claims. In other words, unless a specific order of
steps or actions is specified, the order and/or use of specific
steps and/or actions may be modified without departing from the
scope of the claims.
[0101] The various operations of methods described above may be
performed by any suitable means capable of performing the
corresponding functions. The means may include various hardware
and/or software component(s) and/or module(s), including, but not
limited to a circuit, an application specific integrated circuit
(ASIC), or processor. Software shall be construed broadly to mean
instructions, data, code, or any combination thereof, whether
referred to as software, firmware, middleware, code, microcode,
hardware description language, machine language, or otherwise.
Generally, where there are operations illustrated in Figures, those
operations may be performed by any suitable corresponding
counterpart means-plus-function components.
[0102] For example, means for determining, means for assisting,
means for boosting, means for configuring, means for allocating,
means for reducing, and/or means for indicating may include one or
more processors, such as the transmit processor 220,
controller/processor 240, scheduler 246 and/or other processors or
modules of the base station 110 illustrated in FIG. 2. Means for
announcing, means for boosting, means for transmitting and/or means
for receiving may include a transmitter, such as transmit processor
220, TX MIMO processor 230, receive processor 238, MIMO detector
2366, modulator(s)/demodulator(s) 232a-232t, and/or antenna(s)
234a-234t of the base station 110 illustrated in FIG. 2. Means for
exiting, means for taking, means for coordinating, means for
performing, means for monitoring, means for searching, means for
terminating, means for reducing, means for returning, means for
determining and/or means for indicating may include one or more
processors, such as the receive processor 258, the
controller/processor 280 and/or other processors or modules of the
user terminal 120 illustrated in FIG. 2. Means for receiving and/or
means for transmitting may include receiver processor 258, MIMO
detector 256, transmit processor 264, transmit MIMO processor 266,
modulator(s)/demodulator(s) 254a-254r, and/or antenna(s) 252a-252r
of the user terminal 120 illustrated in FIG. 2.
[0103] Those of skill in the art would understand that information
and signals may be represented using any of a variety of different
technologies and techniques. For example, data, instructions,
commands, information, signals, bits, symbols, and chips that may
be referenced throughout the above description may be represented
by voltages, currents, electromagnetic waves, magnetic fields or
particles, optical fields or particles, or combinations
thereof.
[0104] Those of skill would further appreciate that the various
illustrative logical blocks, modules, circuits, and algorithm steps
described in connection with the disclosure herein may be
implemented as hardware, software, or combinations thereof. To
clearly illustrate this interchangeability of hardware and
software, various illustrative components, blocks, modules,
circuits, and steps have been described above generally in terms of
their functionality. Whether such functionality is implemented as
hardware or software depends upon the particular application and
design constraints imposed on the overall system. Skilled artisans
may implement the described functionality in varying ways for each
particular application, but such implementation decisions should
not be interpreted as causing a departure from the scope of the
present disclosure.
[0105] The various illustrative logical blocks, modules, and
circuits described in connection with the disclosure herein may be
implemented or performed with a general-purpose processor, a
digital signal processor (DSP), an application specific integrated
circuit (ASIC), a field programmable gate array (FPGA) or other
programmable logic device, discrete gate or transistor logic,
discrete hardware components, or any combination thereof designed
to perform the functions described herein. A general-purpose
processor may be a microprocessor, but in the alternative, the
processor may be any conventional processor, controller,
microcontroller, or state machine. A processor may also be
implemented as a combination of computing devices, e.g., a
combination of a DSP and a microprocessor, a plurality of
microprocessors, one or more microprocessors in conjunction with a
DSP core, or any other such configuration.
[0106] The steps of a method or algorithm described in connection
with the disclosure herein may be embodied directly in hardware, in
a software module executed by a processor, or in a combination
thereof. A software module may reside in RAM memory, flash memory,
ROM memory, EPROM memory, EEPROM memory, phase change memory (PCM),
registers, hard disk, a removable disk, a CD-ROM, or any other form
of storage medium known in the art. An exemplary storage medium is
coupled to the 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. The processor and the storage medium may reside in an
ASIC. The ASIC may reside in a user terminal. In the alternative,
the processor and the storage medium may reside as discrete
components in a user terminal.
[0107] In one or more exemplary designs, the functions described
may be implemented in hardware, software, or combinations thereof.
If implemented in software, the functions may be stored on or
transmitted over as one or more instructions or code on a
computer-readable medium. Computer-readable media includes both
computer storage media and communication media including any medium
that facilitates transfer of a computer program from one place to
another. A storage media may be any available media that can be
accessed by a general purpose or special purpose computer. By way
of example, and not limitation, such computer-readable media can
comprise RAM, ROM, EEPROM, CD/DVD or other optical disk storage,
magnetic disk storage or other magnetic storage devices, or any
other medium that can be used to carry or store desired program
code means in the form of instructions or data structures and that
can be accessed by a general-purpose or special-purpose computer,
or a general-purpose or special-purpose processor. 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, 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, includes
compact disc (CD), laser disc, optical disc, digital versatile disc
(DVD), floppy disk and Blu-ray disc where disks usually reproduce
data magnetically, while discs reproduce data optically with
lasers. Combinations of the above should also be included within
the scope of computer-readable media.
[0108] The previous description of the disclosure is provided to
enable any person skilled in the art to make or use the disclosure.
Various modifications to the disclosure will be readily apparent to
those skilled in the art, and the generic principles defined herein
may be applied to other variations without departing from the
spirit or scope of the disclosure. Thus, the disclosure is not
intended to be limited to the examples and designs described herein
but is to be accorded the widest scope consistent with the
principles and novel features disclosed herein.
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