U.S. patent number 9,271,199 [Application Number 14/088,018] was granted by the patent office on 2016-02-23 for managing system frame numbers (sfns) for circuit-switched fallback (csfb).
This patent grant is currently assigned to QUALCOMM INCORPORATED. The grantee listed for this patent is QUALCOMM Incorporated. Invention is credited to Tom Chin, Guangming Shi, Ming Yang.
United States Patent |
9,271,199 |
Yang , et al. |
February 23, 2016 |
Managing system frame numbers (SFNs) for circuit-switched fallback
(CSFB)
Abstract
A method of wireless communication includes recording an
absolute system frame number (SFN) of a target radio access
technology (RAT) and/or recording a relative system frame number
(SFN) difference between a serving radio access technology (RAT)
and the target RAT. A transmission time interval (TTI) boundary, is
determined after redirection, based at least in part on the
recorded absolute frame number (SFN) and/or the recorded relative
system frame number (SFN) difference.
Inventors: |
Yang; Ming (San Diego, CA),
Chin; Tom (San Diego, CA), Shi; Guangming (San Diego,
CA) |
Applicant: |
Name |
City |
State |
Country |
Type |
QUALCOMM Incorporated |
San Diego |
CA |
US |
|
|
Assignee: |
QUALCOMM INCORPORATED (San
Diego, CA)
|
Family
ID: |
51946004 |
Appl.
No.: |
14/088,018 |
Filed: |
November 22, 2013 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20150148043 A1 |
May 28, 2015 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04W
36/0088 (20130101); H04W 36/0066 (20130101); H04W
36/0022 (20130101); H04W 88/06 (20130101) |
Current International
Class: |
H04W
36/00 (20090101); H04W 88/06 (20090101) |
Field of
Search: |
;455/437 ;370/338 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1983652 |
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Oct 2008 |
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EP |
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2012162673 |
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Nov 2012 |
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WO |
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Other References
International Search Report and Written
Opinion--PCT/US2014/062846--ISA/EPO--Feb. 3, 2015. cited by
applicant.
|
Primary Examiner: Batista; Marcos
Attorney, Agent or Firm: Seyfarth Shaw LLP
Claims
What is claimed is:
1. A method of wireless communication, comprising: Recording, by a
user equipment (UE), an absolute system frame number (SFN) of a
target radio access technology (RAT) and/or a relative system frame
number (SFN) difference between a serving radio access technology
(RAT) and the target RAT; and determining, by the UE, a
transmission time interval (TTI) boundary, after redirection, based
at least in part on the recorded absolute system frame number (SFN)
and/or the recorded relative system frame number (SFN)
difference.
2. The method of claim 1, further comprising skipping blind
decoding of a broadcast control channel (BCCH) in the target RAT to
read a SFN to determine the TTI boundary.
3. The method of claim 1, in which the serving RAT is Long Term
Evolution (LTE).
4. The method of claim 1, in which the target RAT is time
division-synchronous code division multiple access (TD-SCDMA).
5. The method of claim 1, further comprising storing the recorded
difference.
6. The method of claim 1, in which recording the SFN difference
occurs while camped in the target RAT.
7. The method of claim 1, in which recording the SFN difference
occurs during an inter-radio access technology (IRAT)
measurement.
8. An apparatus for wireless communication, comprising: means for
recording an absolute system frame number (SFN) of a target radio
access technology (RAT) and/or a relative system frame number (SFN)
difference between a serving radio access technology (RAT) and the
target RAT; and means for determining a transmission time interval
(TTI) boundary, after redirection, based at least in part on the
recorded absolute system frame number (SFN) and/or the recorded
relative system frame number (SFN) difference.
9. The apparatus of claim 8, further comprising means for skipping
blind decoding of a broadcast control channel (BCCH) in the target
RAT to read a SFN to determine the TTI boundary.
10. The apparatus of claim 8, in which the serving RAT is Long Term
Evolution (LTE).
11. The apparatus of claim 8, in which the target RAT is time
division-synchronous code division multiple access (TD-SCDMA).
12. The apparatus of claim 8, further comprising means for storing
the recorded difference.
13. The apparatus of claim 8, in which the means for recording the
SFN difference occurs while camped in the target RAT.
14. The apparatus of claim 8, in which the means for recording the
SFN difference occurs during an inter-radio access technology
(IRAT) measurement.
15. A non-transitory computer-readable medium having program code
recorded thereon, the program code comprising: program code to
record an absolute system frame number (SFN) of a target radio
access technology (RAT) and/or to record a relative system frame
number (SFN) difference between a serving radio access technology
(RAT) and the target RAT; and program code to determine a
transmission time interval (TTI) boundary, after redirection, based
at least in part on the recorded absolute system frame number (SFN)
and/or the recorded relative system frame number (SFN)
difference.
16. The non-transitory computer-readable medium of claim 15,
further comprising program code to skip blind decoding of a
broadcast control channel (BCCH) in the target RAT to read a SFN to
determine the TTI boundary.
17. The non-transitory computer-readable medium of claim 15, in
which the serving RAT is Long Term Evolution (LTE).
18. The non-transitory computer-readable medium of claim 15, in
which the target RAT is time division-synchronous code division
multiple access (TD-SCDMA).
19. The non-transitory computer-readable medium of claim 15,
further comprising program code to store the recorded
difference.
20. The non-transitory computer-readable medium of claim 15, in
which the program code to record is further configured to record
the SFN difference while a user equipment (UE) is camped in the
target RAT.
21. The non-transitory computer-readable medium of claim 15, in
which the program code to record is further configured to record
the SFN difference during an inter-radio access technology (IRAT)
measurement.
22. An apparatus for wireless communication, comprising: a memory;
and at least one processor coupled to the memory, the at least one
processor being configured: to record an absolute system frame
number (SFN) of a target radio access technology (RAT) and/or to
record a relative system frame number (SFN) difference between a
serving radio access technology (RAT) and the target RAT; and to
determine a transmission time interval (TTI) boundary, after
redirection, based at least in part on the recorded absolute system
frame number (SFN) and/or the recorded relative system frame number
(SFN) difference.
23. The apparatus of claim 22, in which the at least one processor
is further configured to skip blind decoding of a broadcast control
channel (BCCH) in the target RAT to read a SFN to determine the TTI
boundary.
24. The apparatus of claim 22, in which the serving RAT is Long
Term Evolution (LTE).
25. The apparatus of claim 22, in which the target RAT is time
division-synchronous code division multiple access (TD-SCDMA).
26. The apparatus of claim 22, in which the at least one processor
is further configured to store the recorded difference.
27. The apparatus of claim 22, in which the at least one processor
is configured to record the SFN difference occurs while a user
equipment (UE) is camped in the target RAT.
28. The apparatus of claim 22, in which the at least one processor
is configured to record the SFN difference during an inter-radio
access technology (IRAT) measurement.
Description
BACKGROUND
1. Field
Aspects of the present disclosure relate generally to wireless
communication systems, and more particularly, to utilizing system
frame numbers (SFNs) to determine a transmission time interval
(TTI) boundary during redirection from one radio access technology
(RAT) to another.
2. Background
Wireless communication networks are widely deployed to provide
various communication services such as telephony, video, data,
messaging, broadcasts, and so on. Such networks, which are usually
multiple access networks, support communications for multiple users
by sharing the available network resources. One example of such a
network is the Universal Terrestrial Radio Access Network (UTRAN).
The UTRAN is the radio access network (RAN) defined as a part of
the Universal Mobile Telecommunications System (UMTS), a third
generation (3G) mobile phone technology supported by the 3rd
Generation Partnership Project (3GPP). The UMTS, which is the
successor to Global System for Mobile Communications (GSM)
technologies, currently supports various air interface standards,
such as Wideband-Code Division Multiple Access (W-CDMA), Time
Division-Code Division Multiple Access (TD-CDMA), and Time
Division-Synchronous Code Division Multiple Access (TD-SCDMA). For
example, China is pursuing TD-SCDMA as the underlying air interface
in the UTRAN architecture with its existing GSM infrastructure as
the core network. The UMTS also supports enhanced 3G data
communications protocols, such as High Speed Packet Access (HSPA),
which provides higher data transfer speeds and capacity to
associated UMTS networks. HSPA is a collection of two mobile
telephony protocols, High Speed Downlink Packet Access (HSDPA) and
High Speed Uplink Packet Access (HSUPA), that extends and improves
the performance of existing wideband protocols.
As the demand for mobile broadband access continues to increase,
research and development continue to advance the UMTS technologies
not only to meet the growing demand for mobile broadband access,
but to advance and enhance the user experience with mobile
communications.
SUMMARY
In one aspect, a method of wireless communication is disclosed. The
method includes recording an absolute system frame number (SFN) of
a target radio access technology (RAT) and/or a relative system
frame number (SFN) difference between a serving radio access
technology (RAT) and the target RAT. A transmission time interval
(TTI) boundary, after redirection, is then determined based at
least in part on the recorded absolute frame number (SFN) and/or
the recorded relative system frame number (SFN) difference.
Another aspect discloses an apparatus including means for recording
an absolute system frame number (SFN) of a target radio access
technology (RAT) and/or a relative system frame number (SFN)
difference between a serving radio access technology (RAT) and the
target RAT. Also included is a mean for determining a transmission
time interval (TTI) boundary, after redirection, based at least in
part on the recorded absolute frame number (SFN) and/or the
recorded relative system frame number (SFN) difference.
In another aspect, a computer program product for wireless
communications in a wireless network having a non-transitory
computer-readable medium is disclosed. The computer readable medium
has non-transitory program code recorded thereon which, when
executed by the processor(s), causes the processor(s) to perform
operations of recording an absolute system frame number (SFN) of a
target radio access technology (RAT) and/or recording a relative
system frame number (SFN) difference between a serving radio access
technology (RAT) and the target RAT. The program code also causes
the processor(s) to determine a transmission time interval (TTI)
boundary, after redirection, based at least in part on the recorded
absolute frame number (SFN) and/or the recorded relative system
frame number (SFN) difference.
Another aspect discloses wireless communication having a memory and
at least one processor coupled to the memory. The processor(s) is
configured to record an absolute system frame number (SFN) of a
target radio access technology (RAT) and/or record a relative
system frame number (SFN) difference between a serving radio access
technology (RAT) and the target RAT. The processor(s) is also
configured to determine a transmission time interval (TTI)
boundary, after redirection, is then determined based at least in
part on the recorded absolute frame number (SFN) and/or the
recorded relative system frame number (SFN) difference.
This has outlined, rather broadly, the features and technical
advantages of the present disclosure in order that the detailed
description that follows may be better understood. Additional
features and advantages of the disclosure will be described below.
It should be appreciated by those skilled in the art that this
disclosure may be readily utilized as a basis for modifying or
designing other structures for carrying out the same purposes of
the present disclosure. It should also be realized by those skilled
in the art that such equivalent constructions do not depart from
the teachings of the disclosure as set forth in the appended
claims. The novel features, which are believed to be characteristic
of the disclosure, both as to its organization and method of
operation, together with further objects and advantages, will be
better understood from the following description when considered in
connection with the accompanying figures. It is to be expressly
understood, however, that each of the figures is provided for the
purpose of illustration and description only and is not intended as
a definition of the limits of the present disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
The features, nature, and advantages of the present disclosure will
become more apparent from the detailed description set forth below
when taken in conjunction with the drawings in which like reference
characters identify correspondingly throughout.
FIG. 1 is a block diagram conceptually illustrating an example of a
telecommunications system.
FIG. 2 is a block diagram conceptually illustrating an example of a
frame structure in a telecommunications system.
FIG. 3 is a block diagram conceptually illustrating an example of a
node B in communication with a UE in a telecommunications
system.
FIG. 4 illustrates network coverage areas according to aspects of
the present disclosure.
FIG. 5 is a call flow diagram illustrating an aspect of the present
disclosure.
FIG. 6 is a block diagram illustrating a method for determining a
transmission time interval according to one aspect of the present
disclosure.
FIG. 7 is a diagram illustrating an example of a hardware
implementation for an apparatus employing a processing system
according to one aspect of the present disclosure.
DETAILED DESCRIPTION
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 the 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.
Turning now to FIG. 1, a block diagram is shown illustrating an
example of a telecommunications system 100. The various concepts
presented throughout this disclosure may be implemented across a
broad variety of telecommunication systems, network architectures,
and communication standards. By way of example and without
limitation, the aspects of the present disclosure illustrated in
FIG. 1 are presented with reference to a UMTS system employing a
TD-SCDMA standard. In this example, the UMTS system includes a
(radio access network) RAN 102 (e.g., UTRAN) that provides various
wireless services including telephony, video, data, messaging,
broadcasts, and/or other services. The RAN 102 may be divided into
a number of Radio Network Subsystems (RNSs) such as an RNS 107,
each controlled by a Radio Network Controller (RNC) such as an RNC
106. For clarity, only the RNC 106 and the RNS 107 are shown;
however, the RAN 102 may include any number of RNCs and RNSs in
addition to the RNC 106 and RNS 107. The RNC 106 is an apparatus
responsible for, among other things, assigning, reconfiguring and
releasing radio resources within the RNS 107. The RNC 106 may be
interconnected to other RNCs (not shown) in the RAN 102 through
various types of interfaces such as a direct physical connection, a
virtual network, or the like, using any suitable transport
network.
The geographic region covered by the RNS 107 may be divided into a
number of cells, with a radio transceiver apparatus serving each
cell. A radio transceiver apparatus is commonly referred to as a
node B in UMTS applications, but may also be referred to by those
skilled in the art as a base station (BS), a base transceiver
station (BTS), a radio base station, a radio transceiver, a
transceiver function, a basic service set (BSS), an extended
service set (ESS), an access point (AP), or some other suitable
terminology. For clarity, two node Bs 108 are shown; however, the
RNS 107 may include any number of wireless node Bs. The node Bs 108
provide wireless access points to a core network 104 for any number
of mobile apparatuses. Examples of a mobile apparatus include a
cellular phone, a smart phone, a session initiation protocol (SIP)
phone, a laptop, a notebook, a netbook, a smartbook, a personal
digital assistant (PDA), a satellite radio, a global positioning
system (GPS) device, a multimedia device, a video device, a digital
audio player (e.g., MP3 player), a camera, a game console, or any
other similar functioning device. The mobile apparatus is commonly
referred to as user equipment (UE) in UMTS applications, but may
also be referred to by those skilled in the art as a mobile station
(MS), a subscriber station, a mobile unit, a subscriber unit, a
wireless unit, a remote unit, a mobile device, a wireless device, a
wireless communications device, a remote device, a mobile
subscriber station, an access terminal (AT), a mobile terminal, a
wireless terminal, a remote terminal, a handset, a terminal, a user
agent, a mobile client, a client, or some other suitable
terminology. For illustrative purposes, three UEs 110 are shown in
communication with the node Bs 108. The downlink (DL), also called
the forward link, refers to the communication link from a node B to
a UE, and the uplink (UL), also called the reverse link, refers to
the communication link from a UE to a node B.
The core network 104, as shown, includes a GSM core network.
However, as those skilled in the art will recognize, the various
concepts presented throughout this disclosure may be implemented in
a RAN, or other suitable access network, to provide UEs with access
to types of core networks other than GSM networks.
In this example, the core network 104 supports circuit-switched
services with a mobile switching center (MSC) 112 and a gateway MSC
(GMSC) 114. One or more RNCs, such as the RNC 106, may be connected
to the MSC 112. The MSC 112 is an apparatus that controls call
setup, call routing, and UE mobility functions. The MSC 112 also
includes a visitor location register (VLR) (not shown) that
contains subscriber-related information for the duration that a UE
is in the coverage area of the MSC 112. The GMSC 114 provides a
gateway through the MSC 112 for the UE to access a circuit-switched
network 116. The GMSC 114 includes a home location register (HLR)
(not shown) containing subscriber data, such as the data reflecting
the details of the services to which a particular user has
subscribed. The HLR is also associated with an authentication
center (AuC) that contains subscriber-specific authentication data.
When a call is received for a particular UE, the GMSC 114 queries
the HLR to determine the UE's location and forwards the call to the
particular MSC serving that location.
The core network 104 also supports packet-data services with a
serving GPRS support node (SGSN) 118 and a gateway GPRS support
node (GGSN) 120. GPRS, which stands for General Packet Radio
Service, is designed to provide packet-data services at speeds
higher than those available with standard GSM circuit-switched data
services. The GGSN 120 provides a connection for the RAN 102 to a
packet-based network 122. The packet-based network 122 may be the
Internet, a private data network, or some other suitable
packet-based network. The primary function of the GGSN 120 is to
provide the UEs 110 with packet-based network connectivity. Data
packets are transferred between the GGSN 120 and the UEs 110
through the SGSN 118, which performs primarily the same functions
in the packet-based domain as the MSC 112 performs in the
circuit-switched domain.
The UMTS air interface is a spread spectrum Direct-Sequence Code
Division Multiple Access (DS-CDMA) system. The spread spectrum
DS-CDMA spreads user data over a much wider bandwidth through
multiplication by a sequence of pseudorandom bits called chips. The
TD-SCDMA standard is based on such direct sequence spread spectrum
technology and additionally calls for a time division duplexing
(TDD), rather than a frequency division duplexing (FDD) as used in
many FDD mode UMTS/W-CDMA systems. TDD uses the same carrier
frequency for both the uplink (UL) and downlink (DL) between a node
B 108 and a UE 110, but divides uplink and downlink transmissions
into different time slots in the carrier.
FIG. 2 shows a frame structure 200 for a TD-SCDMA carrier. The
TD-SCDMA carrier, as illustrated, has a frame 202 that is 10 ms in
length. The chip rate in TD-SCDMA is 1.28 Mcps. The frame 202 has
two 5 ms subframes 204, and each of the subframes 204 includes
seven time slots, TS0 through TS6. The first time slot, TS0, is
usually allocated for downlink communication, while the second time
slot, TS1, is usually allocated for uplink communication. The
remaining time slots, TS2 through TS6, may be used for either
uplink or downlink, which allows for greater flexibility during
times of higher data transmission times in either the uplink or
downlink directions. A downlink pilot time slot (DwPTS) 206, a
guard period (GP) 208, and an uplink pilot time slot (UpPTS) 210
(also known as the uplink pilot channel (UpPCH)) are located
between TS0 and TS1. Each time slot, TS0-TS6, may allow data
transmission multiplexed on a maximum of 16 code channels. Data
transmission on a code channel includes two data portions 212 (each
with a length of 352 chips) separated by a midamble 214 (with a
length of 144 chips) and followed by a guard period (GP) 216 (with
a length of 16 chips). The midamble 214 may be used for features,
such as channel estimation, while the guard period 216 may be used
to avoid inter-burst interference. Also transmitted in the data
portion is some Layer 1 control information, including
Synchronization Shift (SS) bits 218. Synchronization Shift bits 218
only appear in the second part of the data portion. The
Synchronization Shift bits 218 immediately following the midamble
can indicate three cases: decrease shift, increase shift, or do
nothing in the upload transmit timing. The positions of the SS bits
218 are not generally used during uplink communications.
FIG. 3 is a block diagram of a node B 310 in communication with a
UE 350 in a RAN 300, where the RAN 300 may be the RAN 102 in FIG.
1, the node B 310 may be the node B 108 in FIG. 1, and the UE 350
may be the UE 110 in FIG. 1. In the downlink communication, a
transmit processor 320 may receive data from a data source 312 and
control signals from a controller/processor 340. The transmit
processor 320 provides various signal processing functions for the
data and control signals, as well as reference signals (e.g., pilot
signals). For example, the transmit processor 320 may provide
cyclic redundancy check (CRC) codes for error detection, coding and
interleaving to facilitate forward error correction (FEC), 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), and the like), spreading with orthogonal
variable spreading factors (OVSF), and multiplying with scrambling
codes to produce a series of symbols. Channel estimates from a
channel processor 344 may be used by a controller/processor 340 to
determine the coding, modulation, spreading, and/or scrambling
schemes for the transmit processor 320. These channel estimates may
be derived from a reference signal transmitted by the UE 350 or
from feedback contained in the midamble 214 (FIG. 2) from the UE
350. The symbols generated by the transmit processor 320 are
provided to a transmit frame processor 330 to create a frame
structure. The transmit frame processor 330 creates this frame
structure by multiplexing the symbols with a midamble 214 (FIG. 2)
from the controller/processor 340, resulting in a series of frames.
The frames are then provided to a transmitter 332, which provides
various signal conditioning functions including amplifying,
filtering, and modulating the frames onto a carrier for downlink
transmission over the wireless medium through smart antennas 334.
The smart antennas 334 may be implemented with beam steering
bidirectional adaptive antenna arrays or other similar beam
technologies.
At the UE 350, a receiver 354 receives the downlink transmission
through an antenna 352 and processes the transmission to recover
the information modulated onto the carrier. The information
recovered by the receiver 354 is provided to a receive frame
processor 360, which parses each frame, and provides the midamble
214 (FIG. 2) to a channel processor 394 and the data, control, and
reference signals to a receive processor 370. The receive processor
370 then performs the inverse of the processing performed by the
transmit processor 320 in the node B 310. More specifically, the
receive processor 370 descrambles and despreads the symbols, and
then determines the most likely signal constellation points
transmitted by the node B 310 based on the modulation scheme. These
soft decisions may be based on channel estimates computed by the
channel processor 394. The soft decisions are then decoded and
deinterleaved to recover the data, control, and reference signals.
The CRC codes are then checked to determine whether the frames were
successfully decoded. The data carried by the successfully decoded
frames will then be provided to a data sink 372, which represents
applications running in the UE 350 and/or various user interfaces
(e.g., display). Control signals carried by successfully decoded
frames will be provided to a controller/processor 390. When frames
are unsuccessfully decoded by the receive processor 370, the
controller/processor 390 may also use an acknowledgement (ACK)
and/or negative acknowledgement (NACK) protocol to support
retransmission requests for those frames.
In the uplink, data from a data source 378 and control signals from
the controller/processor 390 are provided to a transmit processor
380. The data source 378 may represent applications running in the
UE 350 and various user interfaces (e.g., keyboard). Similar to the
functionality described in connection with the downlink
transmission by the node B 310, the transmit processor 380 provides
various signal processing functions including CRC codes, coding and
interleaving to facilitate FEC, mapping to signal constellations,
spreading with OVSFs, and scrambling to produce a series of
symbols. Channel estimates, derived by the channel processor 394
from a reference signal transmitted by the node B 310 or from
feedback contained in the midamble transmitted by the node B 310,
may be used to select the appropriate coding, modulation,
spreading, and/or scrambling schemes. The symbols produced by the
transmit processor 380 will be provided to a transmit frame
processor 382 to create a frame structure. The transmit frame
processor 382 creates this frame structure by multiplexing the
symbols with a midamble 214 (FIG. 2) from the controller/processor
390, resulting in a series of frames. The frames are then provided
to a transmitter 356, which provides various signal conditioning
functions including amplification, filtering, and modulating the
frames onto a carrier for uplink transmission over the wireless
medium through the antenna 352.
The uplink transmission is processed at the node B 310 in a manner
similar to that described in connection with the receiver function
at the UE 350. A receiver 335 receives the uplink transmission
through the antenna 334 and processes the transmission to recover
the information modulated onto the carrier. The information
recovered by the receiver 335 is provided to a receive frame
processor 336, which parses each frame, and provides the midamble
214 (FIG. 2) to the channel processor 344 and the data, control,
and reference signals to a receive processor 338. The receive
processor 338 performs the inverse of the processing performed by
the transmit processor 380 in the UE 350. The data and control
signals carried by the successfully decoded frames may then be
provided to a data sink 339 and the controller/processor,
respectively. If some of the frames were unsuccessfully decoded by
the receive processor, the controller/processor 340 may also use an
acknowledgement (ACK) and/or negative acknowledgement (NACK)
protocol to support retransmission requests for those frames.
The controller/processors 340 and 390 may be used to direct the
operation at the node B 310 and the UE 350, respectively. For
example, the controller/processors 340 and 390 may provide various
functions including timing, peripheral interfaces, voltage
regulation, power management, and other control functions. The
computer readable media of memory 392 may store data and software
for the UE 350. For example, the memory 392 of the UE 350 may store
a system frame number (SFN) management module 391 which, when
executed by the controller/processor 390, configures the UE 350 for
recording a relative system frame number difference between a
serving RAT and a target RAT during an IRAT measurement.
System Frame Number (SFN) Handling for Circuit-Switched Fallback
(CSFB)
Some networks, such as a newly deployed network, may cover only a
portion of a geographical area. Another network, such as an older
more established network, may better cover the area, including
remaining portions of the geographical area. FIG. 4 illustrates
coverage of a newly deployed network, such as an LTE network and
also coverage of a more established network, such as a TD-SCDMA
network. A geographical area 400 may include LTE cells 402 and
TD-SCDMA cells 404. A user equipment (UE) 406 may move from one
cell, such as a TD-SCDMA cell 404, to another cell, such as an LTE
cell 402. The movement of the UE 406 may specify a handover or a
cell reselection.
Handover from a first radio access technology (RAT) to a second RAT
may occur for several reasons. First, the network may prefer to
have the user equipment (UE) use the first RAT as a primary RAT and
to use the second RAT for only a specific function, such as for
only voice service(s). Second, there may be coverage holes in the
network of one of the RATs. The handover from the first RAT to the
second RAT may be based on measurement reporting.
Redirection from one RAT to another RAT commonly occurs, for
example, to implement load balancing. Redirection may also be
utilized to implement circuit-switched fallback (CSFB) from one
RAT, such as Long Term Evolution (LTE) to a second RAT, such as
Universal Mobile Telecommunications System (UMTS) frequency
division duplex (FDD), UMTS time division duplex (TDD), or GSM.
Circuit-switched fallback is a feature that enables multimode UEs
that have, for example, third generation (3G)/second generation
(2G) network capabilities in addition to LTE capabilities, to have
circuit switched (CS) voice services while being camped on an LTE
network. A circuit-switched fallback capable UE may initiate a
mobile-originated (MO) circuit-switched (CS) voice call while on
LTE. This results in the UE being moved to a circuit-switched
capable radio access network (RAN), such as a 3G or 2G network for
CS voice call setup. A circuit-switched fallback capable UE may be
paged for a mobile-terminated (MT) voice call while on LTE,
resulting in the UE being moved to a 3G or 2G network for
circuit-switched voice call setup.
Various methods are utilized in attempt to reduce latency that
occurs during circuit-switched fallback call (CFSB) setup. For
example, system information block (SIB) tunneling and deferred
measurement control reading (DMCR) may be introduced to reduce
latency for call setup. For CSFB to UTRAN, the delay related to
call setup may increase due to additional signaling on both the LTE
and UTRAN sides. A substantial part of the call setup delay results
from reading system information on the UTRAN prior to the
access.
The following describes exemplary SIB tunneling and DMCR
implementations that may be utilized to meet operator indicator
specifications for call setup delay. In particular, for the DMCR
implementation, the UE only reads SIBs 1, 3, 5 and 7 prior to
accessing the UTRAN cell for CSFB. The other SIBs, including SIB
11, 12 and 19, are not read prior to accessing the UTRAN for CSFB.
These SIBs (e.g., SIBs 11, 12 and 19) are read again once the UE
returns to an idle mode on the UTRAN cell after the
circuit-switched call setup has been terminated or the
circuit-switched call has ended.
For the SIB tunneling implementation, all of the TD-SCDMA SIBs are
carried in a radio resource control (RRC) release message from the
LTE network. In this implementation, the UE skips reading all of
the SIBs from the TD-SCDMA network. After the UE is redirected to
the TD-SCDMA network by the LTE network, and during TD-SCDMA cell
acquisition, the UE is only aware of a 5 ms sub-frame boundary. The
UE, however, has to find a 20-40 ms transmission time interval
(TTI) boundary after the UE is redirected. Thus, the UE locates the
transmission time interval (TTI) boundary by blindly decoding the
broadcast control channel (BCCH) without knowledge of the BCCH
boundary. However, it takes about 30 to 100 ms for the UE to locate
a 40 ms TTI boundary, which delays initiating of a random access
procedure in TD-SCDMA.
Aspects of the present disclosure are directed to determining the
TTI boundary in a more efficient manner, thereby reducing latency.
In particular, in one aspect of the disclosure, because the system
frame number (SFN) is the same for all TD-SCDMA cells, the network
may indicate a SFN relative difference in the radio resource
control (RRC) release message from the LTE network. The UE can find
the TD-SCDMA SFN based on the relative difference between the LTE
SFN and TD-SCDMA SFN, and then determine the TTI boundary. This
implementation reduces the latency of CSFB to TD-SCDMA setup based
on the SIB tunneling implementation.
In other aspects of the disclosure, the UE records the relative
difference between the TD-SCDMA SFN and the LTE SFN during an IRAT
measurement. After the UE is redirected to the TD-SCDMA network,
the UE determines the TTI boundary based on its record. In this
aspect, the UE skips the blind decoding of the broadcast control
channel (BCCH) of a target RAT to read an SFN in order to determine
the TTI boundary. This implementation also reduces the latency of
CSFB to TD-SCDMA setup based on the SIB tunneling
implementation.
In another aspect, the UE records the absolute SFN of a target RAT.
After redirection, the UE determines the TTI boundary based on the
recorded absolute SFN. In another aspect, the UE records the
absolute SFN and/or relative difference between the TD-SCDMA SFN
and the LTE SFN. The UE then determines the TTI boundary based on
the recorded absolute SFN and/or the recorded relative SFN
difference. The relative difference may be recorded while the UE is
camped in the target RAT. Optionally, the relative difference may
be recorded during and IRAT measurement.
FIG. 5 is a call flow diagram 500 illustrating example
communications of a UE 502 between a TD-SCDMA cell 504 and LTE cell
506. At time 510, the UE 502 is connected to/camped on the LTE cell
506 and is in an idle or connected mode. While in idle/connected
mode, the UE 502 performs IRAT measurements, at time 512.
In a first configuration, the UE records the TD-SCDMA SFN relative
difference between the TD-SCDMA network and LTE network while
performing the IRAT measurements.
At time 514, the UE 502 receives an RRC connection release and is
redirected to the TD-SCDMA network. In a second configuration, the
RRC release message includes the SFN relative difference.
At time 516, the UE 502 then returns to the TD-SCDMA cell 504 and
determines the transmission time interval (TTI). In the first
configuration, the determination is based on the recorded
difference. In the second configuration, the determination is based
on the relative difference signaled in the RRC connection release
message.
FIG. 6 shows a wireless communication method 600 according to one
aspect of the disclosure. A UE records an absolute system frame
number (SFN) of a target radio access technology (RAT) and/or
records the relative SFN difference between a serving RAT and a
target RAT, at block 602. The UE then determines a transmission
time interval (TTI) boundary, after redirection, based the recorded
absolute SFN and/or on the recorded relative difference, at block
604.
FIG. 7 is a diagram illustrating an example of a hardware
implementation for an apparatus 700 employing a processing system
714. The processing system 714 may be implemented with a bus
architecture, represented generally by the bus 724. The bus 724 may
include any number of interconnecting buses and bridges depending
on the specific application of the processing system 714 and the
overall design constraints. The bus 724 links together various
circuits including one or more processors and/or hardware modules,
represented by the processor 722 the modules 702, 704, and the
non-transitory computer-readable medium 726. The bus 724 may also
link various other circuits such as timing sources, peripherals,
voltage regulators, and power management circuits, which are well
known in the art, and therefore, will not be described any
further.
The apparatus includes a processing system 714 coupled to a
transceiver 730. The transceiver 730 is coupled to one or more
antennas 720. The transceiver 730 enables communication with
various other apparatus over a transmission medium. The processing
system 714 includes a processor 722 coupled to a non-transitory
computer-readable medium 726. The processor 722 is responsible for
general processing, including the execution of software stored on
the computer-readable medium 726. The software, when executed by
the processor 722, causes the processing system 714 to perform the
various functions described for any particular apparatus. The
computer-readable medium 726 may also be used for storing data that
is manipulated by the processor 722 when executing software.
The processing system 714 includes a recording module 702 for
recording an absolute system frame number and/or recording relative
system frame number difference. The processing system 714 includes
a determining module 704 for determining a transmission time
interval boundary based on the recording. The modules may be
software modules running in the processor 722, resident/stored in
the computer-readable medium 726, one or more hardware modules
coupled to the processor 722, or some combination thereof. The
processing system 714 may be a component of the UE 350 and may
include the memory 392, and/or the controller/processor 390.
In one configuration, an apparatus such as a UE is configured for
wireless communication including means for recording. In one
aspect, the recording means may be the controller/processor 390,
the memory 392, the SFN management module 391, recording module
702, and/or the processing system 714 configured to perform the
recording means. The UE is also configured to include means for
determining. In one aspect, the determining means may be the
controller/processor 390, the memory 392, SFN management module
391, determining module 704 and/or the processing system 714
configured to perform the determining means. In one aspect the
means functions recited by the aforementioned means. In another
aspect, the aforementioned means may be a module or any apparatus
configured to perform the functions recited by the aforementioned
means.
Several aspects of a telecommunications system has been presented
with reference to TD-SCDMA and LTE. As those skilled in the art
will readily appreciate, various aspects described throughout this
disclosure may be extended to other telecommunication systems,
network architectures and communication standards. By way of
example, various aspects may be extended to other UMTS systems such
as W-CDMA, high speed downlink packet access (HSDPA), high speed
uplink packet access (HSUPA), high speed packet access plus (HSPA+)
and TD-CDMA. Various aspects may also be extended to systems
employing Long Term Evolution (LTE) (in FDD, TDD, or both modes),
LTE-Advanced (LTE-A) (in FDD, TDD, or both modes), CDMA2000,
Evolution-Data Optimized (EV-DO), Ultra Mobile Broadband (UMB),
IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20,
Ultra-Wideband (UWB), Bluetooth, and/or other suitable systems. The
actual telecommunication standard, network architecture, and/or
communication standard employed will depend on the specific
application and the overall design constraints imposed on the
system.
Several processors have been described in connection with various
apparatuses and methods. These processors may be implemented using
electronic hardware, computer software, or any combination thereof.
Whether such processors are implemented as hardware or software
will depend upon the particular application and overall design
constraints imposed on the system. By way of example, a processor,
any portion of a processor, or any combination of processors
presented in this disclosure may be implemented with a
microprocessor, microcontroller, digital signal processor (DSP), a
field-programmable gate array (FPGA), a programmable logic device
(PLD), a state machine, gated logic, discrete hardware circuits,
and other suitable processing components configured to perform the
various functions described throughout this disclosure. The
functionality of a processor, any portion of a processor, or any
combination of processors presented in this disclosure may be
implemented with software being executed by a microprocessor,
microcontroller, DSP, or other suitable platform.
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. The software may reside on a
non-transitory computer-readable medium. A computer-readable medium
may include, by way of example, memory such as a magnetic storage
device (e.g., hard disk, floppy disk, magnetic strip), an optical
disk (e.g., compact disc (CD), digital versatile disc (DVD)), a
smart card, a flash memory device (e.g., card, stick, key drive),
random access memory (RAM), read only memory (ROM), programmable
ROM (PROM), erasable PROM (EPROM), electrically erasable PROM
(EEPROM), a register, or a removable disk. Although memory is shown
separate from the processors in the various aspects presented
throughout this disclosure, the memory may be internal to the
processors (e.g., cache or register).
Computer-readable media may be embodied in a computer-program
product. By way of example, a computer-program product may include
a computer-readable medium in packaging materials. Those skilled in
the art will recognize how best to implement the described
functionality presented throughout this disclosure depending on the
particular application and the overall design constraints imposed
on the overall system.
It is to be understood that the specific order or hierarchy of
steps in the methods disclosed is an illustration of exemplary
processes. Based upon design preferences, it is understood that the
specific order or hierarchy of steps in the methods may be
rearranged. 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 unless specifically
recited therein.
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 of the 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. 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 and b; a and c; b and c; and a, b and
c. 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 under the provisions of 35 U.S.C. .sctn.112, sixth
paragraph, unless the element is expressly recited using the phrase
"means for" or, in the case of a method claim, the element is
recited using the phrase "step for."
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