WO2017084074A1

WO2017084074A1 - Methods and apparatus to improve user equipment camping on an operator preferred network

Info

Publication number: WO2017084074A1
Application number: PCT/CN2015/095051
Authority: WO
Inventors: Jun Deng; Arvind Santhanam; Srivatsa CHIVUKULA; Nitin Pant; Samudra Reddy KARRI; Niranjana BHATTA; Jie Mao; Xiaochen Chen; Jin Tao HOU
Original assignee: Qualcomm Incorporated
Priority date: 2015-11-19
Filing date: 2015-11-19
Publication date: 2017-05-26

Abstract

Aspects of the present disclosure provide an apparatus and techniques for wireless communication by a user equipment (UE). According to aspects, the UE may maintain a list of center frequencies associated with an operator associated with the UE and may scan one or more frequencies based on the maintained list of center frequencies prior to performing a full band scan for a first radio access technology (RAT), in an effort to find a network associated with the operator to camp on.

Description

METHODS AND APPARATUS TO IMPROVE USER EQUIPMENT CAMPING ON AN OPERATOR PREFERRED NETWORK

Field

The present disclosure generally relates to wireless communication by a user equipment (UE) , and methods and apparatus to improve a UE camping on an operator preferred network.

Background

Wireless communication systems are widely deployed to provide various telecommunication services such as telephony, video, data, messaging, and broadcasts. Typical wireless communication systems may employ multiple-access technologies capable of supporting communication with multiple users by sharing available system resources (e.g., bandwidth, transmit power) . Examples of such multiple-access technologies include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, single-carrier frequency divisional multiple access (SC-FDMA) systems, and time division synchronous code division multiple access (TD-SCDMA) systems.

These multiple access technologies have been adopted in various telecommunication standards to provide a common protocol that enables different wireless devices to communicate on a municipal, national, regional, and even global level. An example of an emerging telecommunication standard is Long Term Evolution (LTE) . LTE/LTE-Advanced is a set of enhancements to the Universal Mobile Telecommunications System (UMTS) mobile standard promulgated by Third Generation Partnership Project (3GPP) . It is designed to better support mobile broadband Internet access by improving spectral efficiency, lower costs, improve services, make use of new spectrum, and better integrate with other open standards using OFDMA on the downlink (DL) , SC-FDMA on the uplink (UL) , and multiple-input multiple-output (MIMO) antenna technology. However, as the demand for mobile broadband access continues to increase, there exists a need for further improvements in LTE technology. Preferably, these improvements should be applicable to other multi- access technologies and the telecommunication standards that employ these technologies.

A UE may be located within the coverage of multiple wireless networks supported by multiple operators. In certain scenarios, the operator associated with the UE (e.g., a home operator) may not have roaming agreements with at least some of the wireless networks in the coverage area of the UE. Techniques and apparatus may be desired for the UE to efficiently find a network on which to camp (e.g., which is supported by its home operator) .

SUMMARY

Certain aspects of the present disclosure provide a method for wireless communication by a UE. The UE may maintain a list of center frequencies associated with an operator associated with the UE and may scan one or more frequencies based on the maintained list of center frequencies associated with the operator associated with the UE prior to performing a full band scan for a first radio access technology (RAT) , in an effort to find a network associated with the operator to camp on.

Aspects generally include methods, apparatus, systems, computer program products, and processing systems, as substantially described herein with reference to and as illustrated by the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary deployment in which multiple wireless networks have overlapping coverage.

FIG. 2 is a diagram illustrating an example of an access network, in accordance with certain aspects of the disclosure.

FIG. 3 is a diagram illustrating an example of a DL frame structure in LTE, in accordance with certain aspects of the disclosure.

FIG. 4 is a diagram illustrating an example of an UL frame structure in LTE, in accordance with certain aspects of the disclosure.

FIG. 5 is a diagram illustrating an example of a radio protocol architecture for the user and control plane, in accordance with certain aspects of the disclosure.

FIG. 6 is a diagram illustrating an example of an evolved Node B (eNB) and user equipment (UE) in an access network, in accordance with certain aspects of the disclosure.

FIG. 7 illustrates example operations performed by UE, in accordance with certain aspects of the disclosure.

FIG. 8 illustrates example timelines for carrier-provisioned frequency list (CFPL) management, in accordance with certain aspects of the present disclosure.

FIG. 9 illustrates exemplary EARFCNs provisioned in CPFLs corresponding to operators, in accordance with certain aspects of the disclosure.

FIG. 10 illustrates example scenarios where the UE may employ the CPFL for scanning, in accordance with certain aspects of the disclosure.

FIG. 11 illustrates example scenarios where a DSDS UE may employ the CPFL for scanning, in accordance with certain aspects of the disclosure.

DETAILED DESCRIPTION

Aspects of the present disclosure provide techniques and apparatus to assist a UE to more efficiently find an operator preferred network on which to camp. As will be explained in more detail herein, a UE may maintain a list of center frequencies associated with an operator associated with the UE (e.g., a carrier-provisioned frequency list (CPFL) ) . In certain scenarios, in an effort to save time and/or resources at the UE, while looking for a network to camp on, the UE may scan one or more frequencies based on the list of center frequencies prior to performing a full band scan.

The detailed description set forth below in connection with the appended drawings is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well-known structures and components are shown in block diagram form in order to avoid obscuring such concepts.

Several aspects of telecommunication systems will now be presented with reference to various apparatus and methods. These apparatus and methods will be described in the following detailed description and illustrated in the accompanying drawings by various blocks, modules, components, circuits, steps, processes, algorithms, etc. (collectively referred to as “elements” ) . These elements may be implemented using hardware, software/firmware, or combinations thereof. Whether such elements are implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system.

By way of example, an element, or any portion of an element, or any combination of elements may be implemented with a “processing system” that includes one or more processors. Examples of processors include microprocessors, microcontrollers, digital signal processors (DSPs) , field programmable gate arrays (FPGAs) , programmable logic devices (PLDs) , state machines, gated logic, discrete hardware circuits, and other suitable hardware configured to perform the various functionality described throughout this disclosure. One or more processors in the processing system may execute software. Software shall be construed broadly to mean instructions, instruction sets, code, code segments, program code, programs, subprograms, software modules, applications, software applications, software packages, routines, subroutines, objects, executables, threads of execution, procedures, functions, etc., whether referred to as software/firmware, middleware, microcode, hardware description language, or otherwise.

Accordingly, in one or more exemplary embodiments, the functions described may be implemented in hardware, software/firmware, or combinations thereof. If implemented in software, the functions may be stored on or encoded as one or more instructions or code on a computer-readable medium. Computer-readable media includes computer storage media. Storage media may be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM 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 in the form of instructions or data structures and that can be accessed by a computer. 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.

The techniques described herein may be used for various wireless communication networks such as code division multiple access (CDMA) , time division multiple access (TDMA) , frequency division multiple access (FDMA) , orthogonal FDMA (OFDMA) , single carrier FDMA (SC-FDMA) and other networks. The terms “network” and “system" ” are often used interchangeably. A CDMA network may implement a radio access technology (RAT) such as universal terrestrial radio access (UTRA) , cdma2000, etc. UTRA includes wideband CDMA (WCDMA) and other variants of CDMA. cdma2000 covers IS-2000, IS-95 and IS-856 standards. IS-2000 is also referred to as 1x radio transmission technology (1xRTT) , CDMA2000 1X, etc. A TDMA network may implement a RAT such as global system for mobile communications (GSM) , enhanced data rates for GSM evolution (EDGE) , or GSM/EDGE radio access network (GERAN) . An OFDMA network may implement a RAT such as evolved UTRA (E-UTRA) , ultra mobile broadband (UMB) , IEEE 802.11 (Wi-Fi) , IEEE 802.16 (WiMAX) , IEEE 802.20, Flash-OFDM. RTM., etc. UTRA and E-UTRA are part of universal mobile telecommunication system (UMTS) . 3GPP long-term evolution (LTE) and LTE-Advanced (LTE-A) are 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-Aand GSM are described in documents from an organization named “3rd Generation Partnership Project” (3GPP) . cdma2000 and UMB are described in documents from an organization named “3rd Generation Partnership Project 2” (3GPP2) . The techniques described herein may be used for the wireless networks and RATs mentioned above as well as other wireless networks and RATs.

FIG. 1 illustrates an example deployment in which aspects of the present disclosure may be implemented. For example, a UE, such as UE 120 may be in the coverage area of multiple radio access technologies (RATs) . The multiple RATs may be supported by one of a network associated with an operator of and/or associated with the UE or a network not supported by the operator of and/or associated with the UE. In certain scenarios, for example, the operator of and/or associated with the UE not having a roaming agreement with non-associated networks, the UE may not be able to acquire services on certain networks. Accordingly, a UE may not be able to camp on such networks. As described herein aspects describe techniques for a UE to scan a list of center frequencies (e.g., a carrier provisioned frequency list) prior to performing a full band scan, in an effort to efficiently find a network on which to camp.

FIG. 1 shows an exemplary deployment in which multiple wireless networks have overlapping coverage. A radio access network such as an evolved universal terrestrial radio access network (E-UTRAN) 120 may support LTE and may include a number of evolved Node Bs (eNBs) 122 and other network entities that can support wireless communication for user equipments (UEs) . Each eNB may provide communication coverage for a particular geographic area. The term “cell” can refer to a coverage area of an eNB and/or an eNB subsystem serving this coverage area. A serving gateway (S-GW) 124 may communicate with E-UTRAN 120 and may perform various functions such as packet routing and forwarding, mobility anchoring, packet buffering, initiation of network-triggered services, etc. A mobility management entity (MME) 126 may communicate with E-UTRAN 120 and serving gateway 124 and may perform various functions such as mobility management, bearer management, distribution of paging messages, security control, authentication, gateway selection, etc. The network entities in LTE are described in 3GPP TS 36.300, entitled “Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN) ； Overall description, ” which is publicly available.

A radio access network (RAN) 130 may support GSM and may include a number of base stations 132 and other network entities that can support wireless communication for UEs. A mobile switching center (MSC) 134 may communicate with the RAN 130 and may support voice services, provide routing for circuit-switched calls, and perform mobility management for UEs located within the area served by MSC 134. Optionally, an inter-working function (IWF) 140 may facilitate communication between MME 126 and MSC 134 (e.g., for 1xCSFB) .

E-UTRAN 120, serving gateway 124, and MME 126 may be part of an LTE network 102. RAN 130 and MSC 134 may be part of a GSM network 104. For simplicity, FIG. 1 shows only some network entities in the LTE network 102 and the GSM network 104. The LTE and GSM networks may also include other network entities that may support various functions and services.

In general, any number of wireless networks may be deployed in a given geographic area. Each wireless network may support a particular RAT and may operate on one or more frequencies. A RAT may also be referred to as a radio technology, an air interface, etc. A frequency may also be referred to as a carrier, a frequency channel, etc. Each frequency may support a single RAT in a given geographic area in order to avoid interference between wireless networks of different RATs.

A UE 110 may be stationary or mobile and may also be referred to as a mobile station, a terminal, an access terminal, a subscriber unit, a station, etc. UE 110 may be 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, etc. In aspects, UE 110 may be a Dual SIM dual standby (DSDS) UE.

Upon power up, UE 110 may search for wireless networks from which it can receive communication services. If more than one wireless network is detected, then a wireless network with the highest priority may be selected to serve UE 110 and may be referred to as the serving network. UE 110 may perform registration with the serving network, if necessary. UE 110 may then operate in a connected mode to actively communicate with the serving network. Alternatively, UE 110 may operate in an idle mode and camp on the serving network if active communication is not required by UE 110.

UE 110 may be located within the coverage of cells of multiple frequencies and/or multiple RATs while in the idle mode. For LTE, UE 110 may select a frequency and a RAT to camp on based on a priority list. This priority list may include a set of frequencies, a RAT associated with each frequency, and a priority of each frequency. For example, the priority list may include three frequencies X, Y and Z. Frequency X may be used for LTE and may have the highest priority, frequency Y may be used for GSM and may have the lowest priority, and frequency Z may also be used for GSM and may have medium priority. In general, the priority list may include any number of frequencies for any set of RATs and may be specific for the UE location. UE 110 may be configured to prefer LTE, when available, by defining the priority list with LTE frequencies at the highest priority and with frequencies for other RATs at lower priorities, e.g., as given by the example above.

UE 110 may operate in the idle mode as follows. UE 110 may identify all frequencies/RATs on which it is able to find a “suitable” cell in a normal scenario or an “acceptable” cell in an emergency scenario, where “suitable” and “acceptable” are specified in the LTE standards. UE 110 may then camp on the frequency/RAT with the highest priority among all identified frequencies/RATs. UE 110 may remain camped on this frequency/RAT until either (i) the frequency/RAT is no longer available at a predetermined threshold or (ii) another frequency/RAT with a higher priority reaches this threshold. This operating behavior for UE 110 in the idle mode is described in 3GPP TS 36.304, entitled “Evolved Universal Terrestrial Radio Access (E-UTRA) ； User Equipment (UE) procedures in idle mode, ” which is publicly available.

UE 110 may be able to receive packet-switched (PS) data services from LTE network 102 and may camp on the LTE network while in the idle mode. LTE network 102 may have limited or no support for voice-over-Internet protocol (VoIP) , which may often be the case for early deployments of LTE networks. Due to the limited VoIP support, UE 110 may be transferred to another wireless network of another RAT for voice calls. This transfer may be referred to as circuit-switched (CS) fallback. UE 110 may be transferred to a RAT that can support voice service such as 1xRTT, WCDMA, GSM, etc. For call origination with CS fallback, UE 110 may initially become connected to a wireless network of a source RAT (e.g., LTE) that may not support voice service. The UE may originate a voice call with this wireless network and may be transferred through higher-layer signaling to another wireless network of a target RAT that can support the voice call. The higher-layer signaling to transfer the UE to the target RAT may be for various procedures, e.g., connection release with redirection, PS handover, etc.

FIG. 2 is a diagram illustrating an example of an access network 200 in an LTE network architecture. In this example, the access network 200 is divided into a number of cellular regions (cells) 202. One or more lower power class eNBs 208 may have cellular regions 210 that overlap with one or more of the cells 202. A lower power class eNB 208 may be referred to as a remote radio head (RRH) . The lower power class eNB 208 may be a femto cell (e.g., home eNB (HeNB) ) , pico cell, or micro cell. The macro eNBs 204 are each assigned to a respective cell 202 and are configured to provide an access point to the EPC 110 for all the UEs 206 in the cells 202. There is no centralized controller in this example of an access network 200, but a centralized controller may be used in alternative configurations. The eNBs 204 are responsible for all radio related functions including radio bearer control, admission control, mobility control, scheduling, security, and connectivity to the serving gateway 124.

The modulation and multiple access scheme employed by the access network 200 may vary depending on the particular telecommunications standard being deployed. In LTE applications, OFDM is used on the DL and SC-FDMA is used on the UL to support both frequency division duplexing (FDD) and time division duplexing (TDD) . As those skilled in the art will readily appreciate from the detailed description to follow, the various concepts presented herein are well suited for LTE applications. However, these concepts may be readily extended to other telecommunication standards employing other modulation and multiple access techniques. By way of example, these concepts may be extended to Evolution-Data Optimized (EV-DO) or Ultra Mobile Broadband (UMB) . EV-DO and UMB are air interface standards promulgated by the 3rd Generation Partnership Project 2 (3GPP2) as part of the CDMA2000 family of standards and employs CDMA to provide broadband Internet access to mobile stations. These concepts may also be extended to Universal Terrestrial Radio Access (UTRA) employing Wideband-CDMA (W-CDMA) and other variants of CDMA, such as TD-SCDMA； Global System for Mobile Communications (GSM) employing TDMA； and Evolved UTRA (E-UTRA) , Ultra Mobile Broadband (UMB) , IEEE 802.11 (Wi-Fi) , IEEE 802.16 (WiMAX) , IEEE 802.20, and Flash-OFDM employing OFDMA. UTRA, E-UTRA, UMTS, LTE and GSM are described in documents from the 3GPP organization. CDMA2000 and UMB are described in documents from the 3GPP2 organization. The actual wireless communication standard and the multiple access technology employed will depend on the specific application and the overall design constraints imposed on the system.

The eNBs 204 may have multiple antennas supporting MIMO technology. The use of MIMO technology enables the eNBs 204 to exploit the spatial domain to support spatial multiplexing, beamforming, and transmit diversity. Spatial multiplexing may be used to transmit different streams of data simultaneously on the same frequency. The data steams may be transmitted to a single UE 206 to increase the data rate or to multiple UEs 206 to increase the overall system capacity. This is achieved by spatially precoding each data stream (e.g., applying a scaling of an amplitude and a phase) and then transmitting each spatially precoded stream through multiple transmit antennas on the DL. The spatially precoded data streams arrive at the UE (s) 206 with different spatial signatures, which enables each of the UE (s) 206 to recover the one or more data streams destined for that UE 206. On the UL, each UE 206 transmits a spatially precoded data stream, which enables the eNB 204 to identify the source of each spatially precoded data stream.

Spatial multiplexing is generally used when channel conditions are good. When channel conditions are less favorable, beamforming may be used to focus the transmission energy in one or more directions. This may be achieved by spatially precoding the data for transmission through multiple antennas. To achieve good coverage at the edges of the cell, a single stream beamforming transmission may be used in combination with transmit diversity.

In the detailed description that follows, various aspects of an access network will be described with reference to a MIMO system supporting OFDM on the DL. OFDM is a spread-spectrum technique that modulates data over a number of subcarriers within an OFDM symbol. The subcarriers are spaced apart at precise frequencies. The spacing provides “orthogonality” that enables a receiver to recover the data from the subcarriers. In the time domain, a guard interval (e.g., cyclic prefix) may be added to each OFDM symbol to combat inter-OFDM-symbol interference. The UL may use SC-FDMA in the form of a DFT-spread OFDM signal to compensate for high peak-to-average power ratio (PAPR) .

FIG. 3 is a diagram 300 illustrating an example of a DL frame structure in LTE. A frame (10 ms) may be divided into 10 equally sized sub-frames with indices of 0 through 9. Each sub-frame may include two consecutive time slots. A resource grid may be used to represent two time slots, each time slot including a resource block. The resource grid is divided into multiple resource elements. In LTE, a resource block contains 12 consecutive subcarriers in the frequency domain and, for a normal cyclic prefix in each OFDM symbol, 7 consecutive OFDM symbols in the time domain, or 84 resource elements. For an extended cyclic prefix, a resource block contains 6 consecutive OFDM symbols in the time domain and has 72 resource elements. Some of the resource elements, as indicated as

R

302, 304, include DL reference signals (DL-RS). The DL-RS include Cell-specific RS (CRS) (also sometimes called common RS) 302 and UE-specific RS (UE-RS) 304. UE-RS 304 are transmitted only on the resource blocks upon which the corresponding physical DL shared channel (PDSCH) is mapped. The number of bits carried by each resource element depends on the modulation scheme. Thus, the more resource blocks that a UE receives and the higher the modulation scheme, the higher the data rate for the UE.

In LTE, an eNB may send a primary synchronization signal (PSS) and a secondary synchronization signal (SSS) for each cell in the eNB. The primary and secondary synchronization signals may be sent in

symbol periods

6 and 5, respectively, in each of

subframes

0 and 5 of each radio frame with the normal cyclic prefix (CP) . The synchronization signals may be used by UEs for cell detection and acquisition. The eNB may send a Physical Broadcast Channel (PBCH) in symbol periods 0 to 3 in slot 1 of subframe 0. The PBCH may carry certain system information.

The eNB may send a Physical Control Format Indicator Channel (PCFICH) in the first symbol period of each subframe. The PCFICH may convey the number of symbol periods (M) used for control channels, where M may be equal to 1, 2 or 3 and may change from subframe to subframe. M may also be equal to 4 for a small system bandwidth, e.g., with less than 10 resource blocks. The eNB may send a Physical HARQ Indicator Channel (PHICH) and a Physical Downlink Control Channel (PDCCH) in the first M symbol periods of each subframe. The PHICH may carry information to support hybrid automatic repeat request (HARQ) . The PDCCH may carry information on resource allocation for UEs and control information for downlink channels. The eNB may send a Physical Downlink Shared Channel (PDSCH) in the remaining symbol periods of each subframe. The PDSCH may carry data for UEs scheduled for data transmission on the downlink.

The eNB may send the PSS, SSS, and PBCH in the center 1.08 MHz of the system bandwidth used by the eNB. The eNB may send the PCFICH and PHICH across the entire system bandwidth in each symbol period in which these channels are sent. The eNB may send the PDCCH to groups of UEs in certain portions of the system bandwidth. The eNB may send the PDSCH to specific UEs in specific portions of the system bandwidth. The eNB may send the PSS, SSS, PBCH, PCFICH, and PHICH in a broadcast manner to all UEs, may send the PDCCH in a unicast manner to specific UEs, and may also send the PDSCH in a unicast manner to specific UEs.

A number of resource elements may be available in each symbol period. Each resource element (RE) may cover one subcarrier in one symbol period and may be used to send one modulation symbol, which may be a real or complex value. Resource elements not used for a reference signal in each symbol period may be arranged into resource element groups (REGs) . Each REG may include four resource elements in one symbol period. The PCFICH may occupy four REGs, which may be spaced approximately equally across frequency, in symbol period 0. The PHICH may occupy three REGs, which may be spread across frequency, in one or more configurable symbol periods. For example, the three REGs for the PHICH may all belong in symbol period 0 or may be spread in

symbol periods

0, 1, and 2. The PDCCH may occupy 9, 18, 36, or 72 REGs, which may be selected from the available REGs, in the first M symbol periods, for example. Only certain combinations of REGs may be allowed for the PDCCH.

A UE may know the specific REGs used for the PHICH and the PCFICH. The UE may search different combinations of REGs for the PDCCH. The number of combinations to search is typically less than the number of allowed combinations for the PDCCH. An eNB may send the PDCCH to the UE in any of the combinations that the UE will search.

FIG. 4 is a diagram 400 illustrating an example of an UL frame structure in LTE. The available resource blocks for the UL may be partitioned into a data section and a control section. The control section may be formed at the two edges of the system bandwidth and may have a configurable size. The resource blocks in the control section may be assigned to UEs for transmission of control information. The data section may include all resource blocks not included in the control section. The UL frame structure results in the data section including contiguous subcarriers, which may allow a single UE to be assigned all of the contiguous subcarriers in the data section.

A UE may be assigned

resource blocks

410a, 410b in the control section to transmit control information to an eNB. The UE may also be assigned

resource blocks

420a, 420b in the data section to transmit data to the eNB. The UE may transmit control information in a physical UL control channel (PUCCH) on the assigned resource blocks in the control section. The UE may transmit only data or both data and control information in a physical UL shared channel (PUSCH) on the assigned resource blocks in the data section. A UL transmission may span both slots of a subframe and may hop across frequency.

A set of resource blocks may be used to perform initial system access and achieve UL synchronization in a physical random access channel (PRACH) 430. The PRACH 430 carries a random sequence and cannot carry any UL data/signaling. Each random access preamble occupies a bandwidth corresponding to six consecutive resource blocks. The starting frequency is specified by the network. That is, the transmission of the random access preamble is restricted to certain time and frequency resources. There is no frequency hopping for the PRACH. The PRACH attempt is carried in a single subframe (1 ms) or in a sequence of few contiguous subframes and a UE can make only a single PRACH attempt per frame (10 ms) .

FIG. 5 is a diagram 500 illustrating an example of a radio protocol architecture for the user and control planes in LTE. The radio protocol architecture for the UE and the eNB is shown with three layers: Layer 1, Layer 2, and Layer 3. Layer 1 (L1 layer) is the lowest layer and implements various physical layer signal processing functions. The L1 layer will be referred to herein as the physical layer 506. Layer 2 (L2 layer) 508 is above the physical layer 506 and is responsible for the link between the UE and eNB over the physical layer 506.

In the user plane, the L2 layer 508 includes a media access control (MAC) sublayer 510, a radio link control (RLC) sublayer 512, and a packet data convergence protocol (PDCP) 514 sublayer, which are terminated at the eNB on the network side. Although not shown, the UE may have several upper layers above the L2 layer 508 including a network layer (e.g., IP layer) that is terminated at the PDN gateway 118 on the network side, and an application layer that is terminated at the other end of the connection (e.g., far end UE, server, etc. ) .

The PDCP sublayer 514 provides multiplexing between different radio bearers and logical channels. The PDCP sublayer 514 also provides header compression for upper layer data packets to reduce radio transmission overhead, security by ciphering the data packets, and handover support for UEs between eNBs. The RLC sublayer 512 provides segmentation and reassembly of upper layer data packets, retransmission of lost data packets, and reordering of data packets to compensate for out-of-order reception due to hybrid automatic repeat request (HARQ) . The MAC sublayer 510 provides multiplexing between logical and transport channels. The MAC sublayer 510 is also responsible for allocating the various radio resources (e.g., resource blocks) in one cell among the UEs. The MAC sublayer 510 is also responsible for HARQ operations.

In the control plane, the radio protocol architecture for the UE and eNB is substantially the same for the physical layer 506 and the L2 layer 508 with the exception that there is no header compression function for the control plane. The control plane also includes a radio resource control (RRC) sublayer 516 in Layer 3 (L3 layer) . The RRC sublayer 516 is responsible for obtaining radio resources (i.e., radio bearers) and for configuring the lower layers using RRC signaling between the eNB and the UE.

FIG. 6 is a block diagram of an eNB 610 in communication with a UE 650 in an access network in accordance with aspects of the present disclosure. The UE 110 of FIG. 1 and/or UE 206 of FIG. 2 may include one or more components of UE 650 as illustrated in FIG. 6. Similarly, the eNBs 122, 132 of FIG. 1 may include one or more components of eNB 610 as illustrated in FIG. 6.

In the DL, upper layer packets from the core network are provided to a controller/processor 675. The controller/processor 675 implements the functionality of the L2 layer. In the DL, the controller/processor 675 provides header compression, ciphering, packet segmentation and reordering, multiplexing between logical and transport channels, and radio resource allocations to the UE 650 based on various priority metrics. The controller/processor 675 is also responsible for HARQ operations, retransmission of lost packets, and signaling to the UE 650.

The TX processor 616 implements various signal processing functions for the L1 layer (i.e., physical layer) . The signal processing functions includes coding and interleaving to facilitate forward error correction (FEC) at the UE 650 and mapping to signal constellations based on various modulation schemes (e.g., binary phase-shift keying (BPSK) , quadrature phase-shift keying (QPSK) , M-phase-shift keying (M-PSK) , M-quadrature amplitude modulation (M-QAM) ) . The coded and modulated symbols are then split into parallel streams. Each stream is then mapped to an OFDM subcarrier, multiplexed with a reference signal (e.g., pilot) in the time and/or frequency domain, and then combined together using an Inverse Fast Fourier Transform (IFFT) to produce a physical channel carrying a time domain OFDM symbol stream. The OFDM stream is spatially precoded to produce multiple spatial streams. Channel estimates from a channel estimator 674 may be used to determine the coding and modulation scheme, as well as for spatial processing. The channel estimate may be derived from a reference signal and/or channel condition feedback transmitted by the UE 650. Each spatial stream is then provided to a different antenna 620 via a separate transmitter 618TX. Each transmitter 618TX modulates an RF carrier with a respective spatial stream for transmission.

At the UE 650, each receiver 654RX receives a signal through its respective antenna 652. Each receiver 654RX recovers information modulated onto an RF carrier and provides the information to the receiver (RX) processor 656. The RX processor 656 implements various signal processing functions of the L1 layer. The RX processor 656 performs spatial processing on the information to recover any spatial streams destined for the UE 650. If multiple spatial streams are destined for the UE 650, they may be combined by the RX processor 656 into a single OFDM symbol stream. The RX processor 656 then converts the OFDM symbol stream from the time-domain to the frequency domain using a Fast Fourier Transform (FFT) . The frequency domain signal comprises a separate OFDM symbol stream for each subcarrier of the OFDM signal. The symbols on each subcarrier, and the reference signal, is recovered and demodulated by determining the most likely signal constellation points transmitted by the eNB 610. These soft decisions may be based on channel estimates computed by the channel estimator 658. The soft decisions are then decoded and deinterleaved to recover the data and control signals that were originally transmitted by the eNB 610 on the physical channel. The data and control signals are then provided to the controller/processor 659.

The controller/processor 659 implements the L2 layer. The controller/processor 659 can be associated with a memory 660 that stores program codes and data. The memory 660 may be referred to as a computer-readable medium. In the UL, the controller/processor 659 provides demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, control signal processing to recover upper layer packets from the core network. The upper layer packets are then provided to a data sink 662, which represents all the protocol layers above the L2 layer. Various control signals may also be provided to the data sink 662 for L3 processing. The controller/processor 659 is also responsible for error detection using an acknowledgement (ACK) and/or negative acknowledgement (NACK) protocol to support HARQ operations.

In the UL, a data source 667 is used to provide upper layer packets to the controller/processor 659. The data source 667 represents all protocol layers above the L2 layer. Similar to the functionality described in connection with the DL transmission by the eNB 610, the controller/processor 659 implements the L2 layer for the user plane and the control plane by providing header compression, ciphering, packet segmentation and reordering, and multiplexing between logical and transport channels based on radio resource allocations by the eNB 610. The controller/processor 659 is also responsible for HARQ operations, retransmission of lost packets, and signaling to the eNB 610.

Channel estimates derived by a channel estimator 658 from a reference signal or feedback transmitted by the eNB 610 may be used by the TX processor 668 to select the appropriate coding and modulation schemes, and to facilitate spatial processing. The spatial streams generated by the TX processor 668 are provided to different antenna 652 via separate transmitters 654TX. Each transmitter 654TX modulates an RF carrier with a respective spatial stream for transmission.

The UL transmission is processed at the eNB 610 in a manner similar to that described in connection with the receiver function at the UE 650. Each receiver 618RX receives a signal through its respective antenna 620. Each receiver 618RX recovers information modulated onto an RF carrier and provides the information to a RX processor 670. The RX processor 670 may implement the L1 layer.

The controller/processor 675 implements the L2 layer. The controller/processor 675 can be associated with a memory 676 that stores program codes and data. The memory 676 may be referred to as a computer-readable medium. In the UL, the controller/processor 675 provides demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, control signal processing to recover upper layer packets from the UE 650. Upper layer packets from the controller/processor 675 may be provided to the core network. The controller/processor 675 is also responsible for error detection using an ACK and/or NACK protocol to support HARQ operations.

The controllers/processors 659 may direct the operation at the UE 650. The controller/processor 659 and/or other processors, components, and/or modules at the UE 650 may perform or direct operations performed by the UE as described herein, for example, as illustrated in FIG. 7. In aspects, one or more of any of the components shown in FIG. 6 may be employed to perform example operations 700 and other UE operations for the techniques described herein.

EXAMPLE METHODS AND APPARATUS FOR SCANNING CARRIER-PROVISIONED FREQUENCY LISTS (CPFLs)

For example, upon experiencing a loss of signal, a UE may scan one or more frequency bands in an effort to find a suitable cell on which to camp. For example, the UE may scan a cache of recently seen networks (e.g., the UE may scan frequencies included in an acquisition database) , which may be stored in the UE. The acquisition database may enable fast access because it may include the E-UTRA Absolute Radio Frequency Channel Numbers (EARFCNs) that the UE has recently seen (e.g., during scans) ； however, the acquisition database may only include a limited number of entries (e.g., may be limited to 10 entries) . Furthermore, the UE may or may not have attached to networks stored in the acquisition database, and therefore, may not facilitate fast access. Increasing the number of included EARFCNs included in the acquisition database may increase delays in detecting and camping on a desired network. Notably, it may not be desirable for the UE to delete EARFCNs associated with a home operator.

After scanning the acquisition database, the UE may scan a neighbor cell related information database (e.g., the UE may scan a System Information Block Type 5 (SIB5) neighbor list) . If the UE did not find a network to camp on as a result of scanning the acquisition database and the SIB5 neighbor list, the UE may perform a full band scan in an effort to find a network on which to camp.

A UE may be able to determine a center frequency for a desired RAT (e.g., LTE) based on information included in the acquisition database and/or SIB5 neighbor list, which may lead to efficient scanning by the UE. When performing a full band scan, however, the UE may not know center frequencies associated with networks. Accordingly, the UE may have a large number of candidate frequencies for a desired network. For at least these reasons, band scans may be more time consuming (e.g., may take up to 4 seconds) for the UE and may use a lot of the UE’s resources.

Further, in certain scenarios, the UE may be in an area when an operator associated with the UE does not have as robust of a network as networks associated with other operators. Therefore, performing a band scan with frequencies ordered by energy may be an ineffective method to find a network associated with a home operator of the UE.

According to aspects of the present disclosure, in an effort to efficiently find a network associated with the home operator of the UE on which to camp, the UE may scan one or more frequencies based on a carrier-provisioned frequency list (CPFL) prior to performing a full band scan. The CPFL may include a list of center frequencies associated with an operator of the UE. For example, the CPFL list may include a list of EARFCNs ordered by energy estimates. According to aspects, the CPFL list may include a list of the UE’s operator EARFCNs in the home country. Scanning EARFCNs may take a short amount of time as compared to band scans because the EARFCNs may already be known. Further, because UEs may be predominantly in their home country, the UE may be able to find a home network faster by scanning the CPFL list as compared to performing a full band scan.

FIG. 7 illustrates example operations 700 which may be performed by a UE according to aspects of the present disclosure. For example, the UE 110 of FIG. 1, which may include one or more components and/or modules of UE 650 of FIG. 6 may perform the operations 700. According to aspects, the controller/processor 659 and memory 660 may perform aspects described herein.

At 702, the UE may maintain a list of center frequencies associated with an operator of the UE. The list of center frequencies may include EARFCNs associated with the home operator of the UE. The list may be pre-provisioned on the UE by the original equipment manufacturer (OEM) for quick, efficient “out-of-the-box” acquisition. Additionally or alternatively, the UE may auto-learn EARFCNs. Thus, the UE may add, delete, and/or update entries based on the learned information. The size of the CPFL may be limited to a finite number of entries based, at least in part, on recency of detecting a network. Additionally or alternative, the UE may updated the CPFL based on over the air (OTA) signaling from an operator. As will be explained in more detail herein, when the UE is in a home mobile country code (MCC) region and/or in full RAT out of service (OOS) , the UE may scan the CPFL. In certain scenarios, if the UE is in a foreign MCC, the UE may not scan the CPFL. However, as will be described below, in some scenarios, a UE such as a Dual SIM dual standby (DSDS) UE may leverage information obtained on one subscription while in a foreign MCC region to determine whether or not to scan the CPFL on another subscription.

At 704, the UE may scan one or more frequencies based on the maintained list of center frequencies prior to performing a full band scan for a RAT, in an effort to find a network associated with the operator associated with and/or of the UE to camp on. In aspects, the maintained list may be stored (e.g., in a memory 660 of the UE 650) . In aspects, the UE may determine it is in a power saving mode, and scanning the one or more frequencies stored in the list of center frequencies associated with the operator associated with the UE comprises scanning the one or more frequencies stored in the list of center frequencies associated with the operator associated with the UE further based on determining the UE is in the power saving mode.

In aspects, the UE may determine it is involved in a blind redirection to at least one of a home mobile country code (MCC) region prior to scanning the one or more frequencies based on the maintained list of center frequencies associated with the operator associated with the UE. In aspects, the UE may determine it is in an area bordering a home mobile country code (MCC) region, and scanning the one or more frequencies stored in the list of center frequencies associated with the operator associated with the UE comprises scanning the one or more frequencies stored in the list of center frequencies associated with the operator associated with the UE further based on determining the UE is in the area bordering a home mobile country code (MCC) region.

FIG. 8 illustrates

example timelines

800A and 800B for CPFL management, according to aspects of the present disclosure. As described above, when trying to find a network to camp on, the UE may scan one or more frequencies based on the CFPL list before it performs a full band scan.

Without the described CPFL based scanning, the UE may declare a radio link failure (RLF) and may be in a RRC connected state. A T311 timer may begin and the UE may scan the acquisition database and SIB5 neighbor list, for example, every 2 seconds. The scans of the acquisition database and SIB5 neighbor list may be interlaced with a full band scan.

According to aspects of the present disclosure, as shown in timeline 800A, the UE my declare RLF and may be in a RRC connected state. At 802, the UE may scan for networks included in the acquisition database and/or SIB5 neighbor list. At 804, the UE may scan one or more frequencies based on the CPFL database. If the UE has not found a network to camp on, at 806, the UE may perform a band scan. While the timeline illustrated at 800A indicates that the LTE band scan may take 2 seconds, in certain scenarios, the band scan may take more or less time. For example, in aspects, the band scan may take up to 4 seconds. The illustrated scanning procedure may repeat in an effort to find a network on which to camp.

As shown in timeline 800B, the UE may declare system loss and be in a RRC idle state. At 808, the UE may scan for networks included in the acquisition database and/or SIB5 neighbor list. At 810, the UE may scan one or more frequencies based on the CPFL database. Thereafter, if the UE has not found a network to camp on, at 812, the UE may perform a band scan. The illustrated scanning procedure may repeat in an effort to find a network on which to camp.

According to aspects, the UE may refrain from re-scanning one or more frequencies based on an EARFCN included in the CPFL which was also included in the acquisition database and/or SIB5 neighbor list. In this way, the UE may reduce and/or avoid duplicate scanning for the EARFCN. Accordingly, when performing the CPFL based scan, the UE may scan one or more frequencies which are not included in the acquisition database and/or SIB5 neighbor list.

According to aspects, the CPFL entries may be ordered based on energy estimates so that the UE may attempt acquisition on the EARFCNs based on energy strength. According to aspects, a UE may attempt, at most 4 Physical Cell IDs (PCIs) per EARFCN, in-line with legacy designs.

For a 1-pass scan design, a UE may perform scans, in-sequence, as described below. First, the UE may scan entries in the acquisition database. The non-access stratum (NAS) requested public land mobile network (PLMN) EARFCNs may be prioritized over other EARFCNs. Next, the UE may scan interfrequency neighbors (e.g., scan the SIB5 EARFCNs) . After scanning interfrequency neighbors, the UE may scan one or more frequencies based on the CPFL EARFCNs, which may be ordered based on energy. As described above, the UE may refrain from scanning a frequency based on and/or included in the CPFL which was scanned in during the acquisition database scan and/or interfrequency neighbor scan. After the CPFL based scan, the UE may perform a band scan, if necessary. Similar to the acquisition database, the band ordering of the band scan may be based on energy strength.

For a 2-pass scan, a UE may perform scans, in sequence, as described below. For the first pass, first, the UE may scan entries in the acquisition database associated with priority bands. NAS requested PLMN EARFCNs may be prioritized over other EARFCNs. Next, the UE may scan interfrequency neighbors (e.g., scan the SIB5 EARFCNs) associated with the priority bands. After scanning interfrequency neighbors associated with priority bands, the UE may scan one or more frequencies based on the CPFL EARFCNs associated with priority bands. As described above, the UE may refrain from scanning a frequency based on and/or included in the CPFL which was scanned in during the acquisition database scan or interfrequency neighbor scan. After the CPFL based scan, the UE may perform a priority band scan, if necessary. In aspects, scanning in the priority band scan may be based on Elementary Files (EFs) .

For the second pass, the UE may scan remaining bands and their associated EARFCNs. First, the UE may scan entries in the acquisition database associated with non-priority bands. NAS requested PLMN EARFCNs may be prioritized over other EARFCNs. Next, the UE may scan interfrequency neighbors (e.g., scan the SIB5 EARFCNs) associated with non-priority bands. After scanning interfrequency neighbors associated with non-priority bands, the UE may scan one or more frequencies based on the CPFL EARFCNs associated with non-priority bands. As described above, the UE may refrain from scanning a frequency included in the CPFL which was scanned in during the scan of the acquisition database and/or interfrequency neighbor list. After the CPFL based scan, the UE may perform a non-priority band scan, if necessary. Similar to the acquisition database, the band ordering of the band scan of non-priority bands may be based on energy strength.

FIG. 9 provides an example 900 of operator EARFCNs provisioned in one or more CPFLs, according to aspects of the present disclosure. A UE may include EARFCN’s in one or more CPFLs associated with multiple operators. The EARFCNs associated with three operators (e.g., China Mobile Communications Systems (CMCC) , China Unicom (CU) , and China Telecom (CT) ) are shown in FIG. 9 for non-limiting, illustrative purposes only of an example CPFL in accordance with aspects of the present disclosure.

According to aspects, the operator may update the list of EARFCNs (e.g., a CPFL) when additional EARFCNs are deployed and/or EARFCNs are no longer used. Additionally or alternatively, the UE may auto-learn EARFCNs supported by a home operator and may modify the CPFL to add, delete, and/or update EARFCNs in the CPFL. For example, the UE, while camped on a frequency of a home operator, may find the operator has added new center frequencies. The UE may add newly-learned center frequencies to the CPFL. According to aspects, the UE may clean-up the CPFL, in an effort to keep the list accurate, current, and relevant. Because the CPFL may include a finite list of entries, the UE may delete a center frequency which it has not found and/or camped on for a certain period of time.

FIG. 10 illustrates example scenarios 1000 where the UE may scan the EARFCNs included in the CPFL in accordance with aspects described herein. Upon power up, if the last known MCC of the UE was a home MCC, the UE may scan one or more frequencies based on the CPFL after scanning the acquisition database and/or SIB5 neighbor list when searching for a network to camp on. The UE may scan one or more frequencies based on the CPFL during full RAT out of service (OOS) or blind redirection when a current MCC is in a whitelist or list of MCC allowed by the UE. The UE may use the CPFL in scenarios illustrated in FIG. 10 and, according to aspects, may not use the CPFL while in a roaming MCC region.

FIG. 11 illustrates example scenarios 1100 where a DSDS UE may employ the CPFL for scanning, in accordance with certain aspects of the disclosure. In certain scenarios, a Dual SIM dual standby (DSDS) UE 110 may implement aspects described herein. A DSDS UE may acquire service on two subscriptions using a single radio resource. When the non-multimode subscription of a DSDS UE is in a home network, a multimode subscription of the DSDS UE may perform a scan using the CPFL (e.g., scan one or more frequencies based on the CPFL) , even if the multimode subscription is in a foreign MCC region. Because one of the subscriptions of the UE may be receiving service using the home operating network, the UE may detect and camp on the home operator network, despite being in a foreign MCC region. Correspondingly, if the non-multimode subscription is not in a home MCC region, the multimode subscription of the UE may not scan the CPFL list.

Not only may a UE determine if it is in a home or foreign MCC region, according to aspects, the UE may determine if it is in a border area of a home or foreign MCC region. In an effort to efficiently find a home network on which to camp, the UE may scan the CPFL list if it is in border area, even if the UE is not currently camped on a home MCC network.

According to one option, while performing scans in a MCC region other than the home MCC region (e.g., included in an MCCWhitelist) a UE may detect one or more frequencies associated with at least one EARFCN that belongs to the MCCWhitelist. If, so, the UE may scan one or more frequencies based on and/or included in the CPFL. In aspects, the UE may continue to scan based on the CPFL until the most recent EARFCN entry in acquisition database that belongs to the MCCWhitelist is at least a threshold number of seconds old (e.g., 600 seconds) .

According to another aspect, cells in border locations may be “fingerprinted. ” For example, cells on GSM, WCDMA, LTE, and/or similar RATs and/or PLMNS wherein a higher priority LTE PLMN exists in a MCC region that is in the MCCWhitelist may be fingerprinted. The UE may scan the CPFL when the UE is camped on any fingerprinted border cell. Optionally, the UE may remember an EARFCN to PLMN mapping for fingerprinted border cells.

According to aspects, in an effort to efficiently utilize resources at the UE, a UE may increase a number of center frequencies scanned in the CPFL as time passes. For a first amount of time of scanning the CPFL, the UE may scan a certain number of center frequencies. If the UE has not found a network to camp on after the first amount of time has passes, the UE may increase the number of center frequencies scanned for a second period of time and so on.

It is understood that the specific order or hierarchy of steps in the processes disclosed is an illustration of exemplary approaches. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the processes may be rearranged. Further, some steps may be combined or omitted. The accompanying method claims present elements of the various steps in a sample order, and are not meant to be limited to the specific order or hierarchy presented.

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) .

The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but is to be accorded the full scope consistent with the language claims, wherein reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more. ” Unless specifically stated otherwise, the term “some” refers to one or more. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed as a means plus function unless the element is expressly recited using the phrase “means for. ”

Claims

A method for wireless communication by a user equipment (UE) , comprising:

maintaining a list of center frequencies associated with an operator associated with the UE； and

scanning one or more frequencies based on the maintained list of center frequencies associated with the operator associated with the UE prior to performing a full band scan for a first radio access technology (RAT) , in an effort to find a network associated with the operator to camp on.
The method of claim 1, further comprising:

determining the UE is in at least one of a home mobile country code (MCC) region or an out of service state prior to scanning the one or more frequencies based on the maintained list of center frequencies associated with the operator associated with the UE.
The method of claim 1, wherein the list of center frequencies associated with an operator associated with the UE comprises one or more carrier-provisioned E-UTRA Absolute Radio Frequency Channel Numbers (EARFCNs) ordered by energy estimates.
The method of claim 1, further comprising:

prior to scanning the one or more frequencies based on the maintained list of center frequencies associated with the operator associated with the UE, scanning frequencies stored in at least one of an acquisition database or inter-frequency neighbor list in an effort to find a network to camp on.
The method of claim 4, wherein scanning the one or more frequencies based on the maintained list of center frequencies associated with the operator associated with the UE comprises:

scanning one or more frequencies not included in at least one of the acquisition database or the inter-frequency neighbor list.
The method of claim 4, further comprising:

when the UE is not located in a home mobile country code (MCC) region, detecting a frequency associated with the home MCC prior to scanning the one or more frequencies based on the maintained list of center frequencies associated with the operator associated with the UE.
The method of 1, further comprising:

dynamically configuring the list of center frequencies.
The method of claim 7, wherein dynamically configuring the list of center frequencies comprises at least one of adding, updating, or deleting a center frequency based, at least in part, on over the air (OTA) signaling or autonomous learning by the UE.
The method of claim 1, wherein scanning the one or more frequencies maintained in the list of center frequencies associated with the operator associated with the UE comprises:

increasing a number of frequencies scanned from the list of center frequencies associated with the operator associated with the UE during subsequent scanning of the one or more frequencies maintained in the list of center frequencies associated with the operator associated with the UE.
The method of claim 1, wherein the UE is a dual SIM dual standby (DSDS) UE and further comprising:

when the UE is located in a foreign mobile country code (MCC) region, scanning the one or more frequencies stored in the list of center frequencies associated with the operator associated with the UE, by a second subscription of the DSDS UE, in response to determining a first subscription of the DSDS UE is camped on a network associated with the operator.
The method of claim 10, further comprising:

determining the UE is in a power saving mode； and

wherein scanning the one or more frequencies stored in the list of center frequencies associated with the operator associated with the UE comprises scanning the one or more frequencies stored in the list of center frequencies associated with the operator associated with the UE further based on determing the UE is in the power saving mode.
The method of claim 1, further comprising:

determining the UE is involved in a blind redirection to at least one of a home mobile country code (MCC) region prior to scanning the one or more frequencies based on the maintained list of center frequencies associated with the operator associated with the UE.
The method of claim 1, further comprising:

determining the UE is in an area bordering a home mobile country code (MCC) region； and

wherein scanning the one or more frequencies stored in the list of center frequencies associated with the operator associated with the UE comprises scanning the one or more frequencies stored in the list of center frequencies associated with the operator associated with the UE further based on determining the UE is in the area bordering a home mobile country code (MCC) region.
A method, apparatus, system, computer program product, and processing system as substantially described herein with reference to and as illustrated by the accompanying drawings.