PATENT DOCUMENT

Publication Number: US-9615377-B2
Application Number: US-201514725764-A
Country: US
Kind Code: B2

Title: Apparatus, systems and methods for prioritizing frequency selection for a mobile device

Abstract:
Described herein are systems and methods for prioritizing frequency selection of a user equipment (“UE”) having a transceiver configured to enable the UE to establish a connection with a network using at least two communication protocols. A method may comprise recording, at the UE, a camped frequency and a camped band with which the UE is communicating with the first network in the first protocol, disconnecting from the first network and connecting to the second network, and disconnecting from the second network and reconnecting to the first network, wherein the reconnecting to the first network includes determining whether one of the camped frequency or a different frequency within the camped band is available for reconnection to the first network, and reconnecting to the first network using the one of the camped frequency or the different frequency within the camped band.

Claims:
The invention claimed is: 
     
       1. A method, comprising:
 at a user equipment (“UE”) having a transceiver configured to enable the UE to establish a connection to a first network at a camped frequency within a camped band using a first protocol and a second network using a second protocol:
 disconnecting from the first network and connecting to the second network; 
 disconnecting from the second network; and 
 performing a cell reselection for reconnection to the first network, wherein the cell reselection includes:
 scanning the camped frequency prior to searching any other frequencies to determine if the camped frequency is available for connection to the first network; 
 connecting to the first network using the camped frequency when the camped frequency is available; 
 scanning different frequencies within the camped band, when the camped frequency is not available, to determine which of the different frequencies within the camped band are available for connection to the first network; 
 connecting to the first network using the one of the different frequencies within the camped band. 
 
 
 
     
     
       2. The method of  claim 1 , wherein determining whether the different frequencies within the camped band are available, comprises:
 performing a cell search in the camped band. 
 
     
     
       3. The method of  claim 1 , further comprising:
 performing a cell search within other frequency bands of the first network when neither the camped frequency nor camped band is available. 
 
     
     
       4. The method of  claim 1 , wherein the first network is a Long Term Evolution (LTE) network. 
     
     
       5. The method of  claim 4 , wherein the LTE network includes a plurality of evolved Node Bs (eNB) and the UE reconnects to the LTE network via one of the plurality of eNBs. 
     
     
       6. The method of  claim 4 , wherein the LTE network supports a time-division duplexing (“TDD”) mode and a frequency-division duplexing (“FDD”) mode. 
     
     
       7. The method of  claim 1 , wherein the second network is one of a GSM, CDMA, CDMA2000, 1×RTT, 1×, and a legacy radio access network. 
     
     
       8. A user equipment (“UE”), comprising:
 a transceiver configured to enable the UE to establish a connection to a first network at a camped frequency within a camped band using a first protocol and a second network using a second protocol; and 
 a processor configured to: 
 instruct the transceiver to disconnect the UE from the first network and connect the UE to the second network; 
 instruct the transceiver to disconnect the UE from the second network; and 
 instruct the transceiver to perform a cell reselection for reconnection to the first network, wherein the cell reselection includes:
 scanning only the camped frequency to determine if the camped frequency is available for connection to the first network; and 
 when the camped frequency is available, connecting to the first network, using the camped frequency. 
 
 
     
     
       9. The UE of  claim 8 , wherein the cell reselection further includes:
 when the camped frequency is not available, scanning only different frequencies within the camped band to determine which of the different frequencies within the camped band are available for connection to the first network; and 
 when at least one of the different frequencies within the camped band is available, connecting to the first network using the one of the different frequencies within the camped band. 
 
     
     
       10. The UE of  claim 9 , wherein the cell reselection further includes:
 when none of the different frequencies within the camped band are available, scanning frequencies outside of the camped band to determine which of the frequencies outside of the camped band are available for connection to the first network; and 
 connecting to the first network using one of the available frequencies outside of the camped band. 
 
     
     
       11. The UE of  claim 8 , wherein the transceiver comprises a plurality of transceivers. 
     
     
       12. The UE of  claim 8 , wherein the first network is a Long Term Evolution (LTE) network. 
     
     
       13. The UE of  claim 12 , wherein the LTE network includes a plurality of evolved Node Bs (eNB) and the UE reconnects to the LTE network via one of the plurality of eNBs. 
     
     
       14. The UE of  claim 12 , wherein the LTE network supports a time-division duplexing (“TDD”) mode and a frequency-division duplexing (“FDD”) mode. 
     
     
       15. The UE of  claim 8 , wherein the second network is one of a GSM, CDMA, CDMA2000, 1×RTT, 1×, and a legacy radio access network. 
     
     
       16. A non-volatile computer-readable medium that stores instructions that, when executed, cause the performance of any action or combination of actions including:
 connecting to a first network at a camped frequency within a camped band; 
 disconnecting from the first network and connecting to a second network; 
 disconnecting from the second network; and 
 performing a cell reselection for reconnection to the first network, wherein the cell reselection includes:
 scanning the camped frequency prior to searching any other frequencies to determine if the camped frequency is available for connection to the first network; 
 connecting to the first network using the camped frequency when the camped frequency is available; 
 scanning different frequencies within the camped band, when the camped frequency is not available, to determine which of the different frequencies within the camped band are available for connection to the first network; 
 connecting to the first network using the one of the different frequencies within the camped band. 
 
 
     
     
       17. The non-volatile computer-readable medium of  claim 16 , wherein determining whether the different frequencies within the camped band are available, comprises:
 performing a cell search in the camped band. 
 
     
     
       18. The non-volatile computer-readable medium of  claim 16 , wherein the actions further include:
 performing a cell search within other frequency bands of the first network when neither the camped frequency nor the different frequencies within the camped band are available for connection to the first network.

Description:
BACKGROUND 
     In wireless telecommunication networks, the Long-Term Evolution, or “LTE,” is defined as a standard for wireless communication of high-speed data for mobile phones and data terminals. The LTE standard is developed by the Third Generation Partnership Project (“3GPP”) and the Institute of Electrical and Electronics Engineers (“IEEE”). An exemplary LTE access network is a wireless network of base stations, or evolved NodeBs (“eNBs”), that are interconnected without a centralized intelligent controller. By distributing the intelligence among the eNBs in the LTE network, the time for setting up a connection with a mobile device (e.g., user equipment (“UE”)) is reduced as well as the time required for a handover to another eNB. Furthermore, through the development of the LTE standard, mobile devices are able to increase their capacity and speed using a different radio interface together with core network improvements. 
     As with any Radio Access Technology, an exemplary LTE network may utilize duplex communications, wherein point-to-point transmissions are composed of two connected devices that communicate with one another in both directions. Thus, a duplex system includes two distinct paths, each carrying information in only one direction. Furthermore, the exemplary LTE network may also utilize channel access methods in point-to-multipoint transmission, wherein forward and reverse communication channels are divided on the same physical communications medium, such as through time-division duplexing (“TDD”) and frequency-division duplexing (“FDD”). 
     Through the use of TDD and FDD modes, the exemplary LTE system may share the critical resources of time and frequency among mobile subscribers or terminals in the network. FDD uses the idea that the transmission and reception of signals are achieved simultaneously using two different frequencies. Using FDD it is possible to transmit and receive signals simultaneously as the UE is not tuned to the same frequency. TDD may use only a single frequency while sharing the channel between transmission and reception and spacing them apart by multiplexing the two signals on a time basis. TDD mode then shares that single frequency by assigning alternating time slots to transmit and receive operations. Accordingly, TDD is used with data transmissions of a short burst of data in each direction. As the transmission periods are relatively short, no time delay would be noticed on voice transmissions resulting from the time delays introduced by using TDD mode. 
     With each of the modes, there can be associated disadvantages. For instance, the FDD mode can require a large amount of frequency spectrum, generally at least twice the spectrum needed the TDD mode. In addition, there should be adequate spectrum separation between the transmit/receive channels. Furthermore, with FDD, it can be difficult to utilize special antenna techniques like multiple-input multiple-output (“MIMO”) and beamforming, wherein these technologies are a core part of the LTE network strategies for increasing data rates. Specifically, it can be difficult to make antenna bandwidths broad enough to cover both sets of spectrum. 
     The primary advantage of TDD mode can be that, unlike FDD mode, the TDD mode only needs a single channel of frequency spectrum. Furthermore, the TDD mode does not require the use spectrum-inefficient guard bands or channel separations as needed in the FDD mode. However, the downside of TDD mode can be that successful implementation may require a very precise timing and synchronization system at both the transmitter and receiver to ensure that time slots do not overlap or otherwise interfere with one another. 
     SUMMARY 
     Described herein are apparatuses, systems and methods for prioritizing frequency selection of a user equipment (“UE”) having a transceiver configured to enable the UE to establish a connection to a first network at a camped frequency within a camped band using a first protocol and a second network using a second protocol. The methods including disconnecting from the first network and connecting to the second network and disconnecting from the second network and reconnecting to the first network. The reconnecting to the first network including determining whether one of the camped frequency or a different frequency within the camped band is available for reconnection to the first network, and reconnecting to the first network using the one of the camped frequency or the different frequency within the camped band 
     Further described herein is a UE including a a transceiver configured to enable the UE to establish a connection to a first network at a camped frequency within a camped band using a first protocol and a second network using a second protocol. The UE further includes a processor that instructs the transceiver to disconnect the UE from the first network and connect the UE to the second network and instructs the transceiver to disconnect the UE from the second network and reconnect the UE to the first network. The reconnecting to the first network includes scanning only the camped frequency to determine if the camped frequency is available and when the camped frequency is available, reconnecting to the first network using the camped frequency. 
     Further described herein is a non-volatile computer-readable medium that stores instructions that, when executed, cause the performance of any action or combination of actions. The actions may include disconnecting from the first network and connecting to the second network and disconnecting from the second network and reconnecting to the first network. The reconnecting to the first network includes determining whether one of a camped frequency or a different frequency within a camped band is available for reconnection to the first network, and reconnecting to the first network using the one of the camped frequency or the different frequency within the camped band. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an exemplary apparatus  100  for prioritizing cell reselection based on a previously used frequency and/or band by a UE, according to various embodiments described herein. 
         FIG. 2  shows an exemplary system  200  in which a UE that prioritizes cell reselection based on a previously used frequency and/or band may operate, according to various embodiments described herein. 
         FIG. 3  shows an exemplary method for a cell selection process at a mobile device, such as the UE, in a wireless network, such as the LTE network, according to various embodiments described herein. 
         FIG. 4  shows an exemplary method for the UE to perform a cell reselection process to reconnect with the LTE network based on prioritizing a previously used frequency and/or band by the UE, according to various embodiments described herein. 
     
    
    
     DETAILED DESCRIPTION 
     The exemplary embodiments may be further understood with reference to the following description and the appended drawings, wherein like elements are referred to with the same reference numerals. The exemplary embodiments describe an apparatus, system and method for prioritizing a cell reselection procedure based on a previously used frequency and/or band. In the exemplary embodiments, a mobile device will be described as user equipment (“UE”) and the base station will be described as an evolved Node B (“eNB”) base station, which is generally known as being a base station associated with an LTE radio access network (“LTE-RAN”). However, it will be understood by those skilled in the art that UEs and base stations operating in accordance with other network standards may also implement the exemplary embodiments in accordance with the functionalities and principles described herein. 
     As discussed above, the usage of either a TDD mode or a FDD mode in an LTE-RAN offers both advantages and disadvantages. Due to the advantages of both TDD and FDD mode, some network providers (e.g., Sprint, AT&amp;T, Verizon, etc.) operate in both LTE modes. Specifically, network providers would like to use the spectrum capacity efficiently and therefore implement traffic management patterns. For example, an exemplary network provider may propose to use the higher frequency range band of LTE spectrum in TDD mode. This allows the LTE-RAN to have a greater capacity, such that a greater number of subscribers are allowed to maintain a connection with a specific cell, e.g., more subscribers can register or “camp” on a particular cell. Alternatively, operating in the lower frequency band spectrum of LTE in FDD mode may allow for greater cell coverage at the eNBs. 
     In the native LTE environment, operating with both TDD mode and FDD mode may be achieved by assigning the cell reselection priority to respective bands that are broadcasted, such as via system information block type 5 (“SIB5”). One skilled in the art would understand that SIB5 data includes information relevant to inter-frequency cell re-selection, e.g., information about other Evolved Universal Terrestrial Radio Access (“E-UTRA”) frequencies and inter-frequency neighboring cells relevant for cell re-selection. Furthermore, the SIB5 data may include cell re-selection parameters common for a frequency as well as cell specific re-selection parameters. 
     In some instances, the UE may fallback from the LTE-RAN to a legacy radio access network (“RAN”), such as a Code Division Multiple Access (“CDMA”) network or a Global Systems for Mobile communications (“GSM”) network. There may be multiple reasons for the UE falling back to the legacy RAN network. In one exemplary embodiment, a network provider may utilize an enhanced Circuit Switched Fallback (“eCSFB”) infrastructure such that the UE may use the legacy RAN for voice calls, while using the LTE-RAN for data connectivity. Thus, when originating or receiving a voice call, the UE may be connected to the legacy RAN. After the completion of the voice call, the UE may reconnect to the LTE network. 
     In current implementations, the reconnection procedure includes the UE performing a cell search and the UE will camp on the strongest cell and band found during the search. This almost exclusively results in the UE camping on a frequency in the FDD band because the FDD band will be the strongest band. However, this method of cell selection may defeat the traffic management strategy of the network provider. Specifically, as described above, the network provider attempts to distribute the UEs between FDD mode and TDD mode to implement a traffic management strategy. Accordingly, the exemplary embodiments provide an apparatus, a system and a method for prioritizing cell reselection based on a previously used frequency and/or band by the UE. By prioritizing the cell reselection process based on frequency and/or band when the UE is reconnecting to the LTE-RAN, it is more likely that the UE will reconnect in the LTE mode (e.g., FDD or TDD) as the UE previously used when connected to the LTE-RAN (e.g., before the UE connected to the legacy RAN). Because the UE is more likely to reconnect to the LTE-RAN in the same mode, it is less likely that the UE will degrade or defeat the network provider&#39;s traffic management strategy. 
       FIG. 1  shows an exemplary apparatus  100  for prioritizing cell reselection based on a previously used frequency and/or band by a UE, according to various embodiments described herein. The exemplary apparatus  100  may include the mobile device, such as a UE  110 . The UE  110  may represent any electronic device that is configured to perform wireless functionalities. For example, the UE  110  may be a portable device such as a smartphone, a tablet, a phablet, a laptop, a wearable, etc. In another example, the UE  110  may be a client stationary device such as a desktop terminal. The UE  110  may be configured to perform cellular and/or WiFi functionalities. The UE  110  may include a processor  120 , a memory arrangement  130 , a display device  140 , an input/output (“I/O”) device  150 , a transceiver  160 , and other components  170 . The other components  170  may include, for example, an audio input device, an audio output device, a battery that provides a limited power supply, a data acquisition device, ports to electrically connect the UE  110  to other electronic devices, etc. 
     The transceiver  160  may be a hardware component configured to transmit and receive data with network entities, such as the eNB of an LTE-RAN and a legacy base station of a legacy RAN. Thus, the transceiver  160  may include multiple transceivers or may have the capability of operating in different modes. The transceiver  160  may enable communication with the network entities or with other electronic devices directly or indirectly through the wireless network protocol to which the UE  110  is connected. The transceiver  160  may operate on a variety of different frequencies or channels (e.g., set of consecutive frequencies). For example, the transceiver  160  may connect to the legacy RAN using corresponding frequencies and also connect to the LTE-RAN using corresponding frequencies. Those skilled in the art will understand that the set of frequencies that may be used to connect with the various RANs may be set by the standards that govern the various RANs. Thus, an antenna or multiple antennae (not shown) coupled with the transceiver  160  may enable the transceiver  160  to send and receive signals in these frequency bands. 
     The processor  120  may be configured to execute a plurality of applications of the UE  110 . For example, the applications may include a web browser when connected to a communication network via the transceiver  160 . The use of the web browser may entail requesting uplink grants to transmit requests to the web browser or downlink grants to receive data from a website. In another example, the processor  120  may implement a cell reselection application that prioritizes cell reselection based on a previously used frequency and/or band by the UE  110 . As described above, the UE  110  is capable of connection to both the LTE-RAN and a legacy RAN. The cell reselection application prioritizes the cell reselection for the UE  110  when the UE  110  reconnects to the LTE-RAN after connecting to the legacy RAN. 
     It should be noted that the above noted applications being an application (e.g., a program) executed by the processor  120  is only exemplary. The functionality associated with the applications may also be represented as a separate incorporated component of the UE  110  or may be a modular component coupled to the UE  110 , e.g., an integrated circuit with or without firmware. In addition, in some UEs, the functionality described for the processor  120  is split among two processors, a baseband processor and an applications processor. The exemplary embodiments may be implemented in any of these or other configurations of the UE. 
     The memory arrangement  130  may be a hardware component configured to store data related to operations performed by the UE  110 . Specifically, the memory arrangement  130  may store data related to functionalities described herein. The display device  140  may be a hardware component configured to show data to a user while the I/O device  150  may be a hardware component that enables the user to enter inputs. It should be noted that the display device  140  and the I/O device  150  may be separate components or integrated together such as a touchscreen. 
       FIG. 2  shows an exemplary system  200  in which a UE that prioritizes cell reselection based on a previously used frequency and/or band may operate, according to various embodiments described herein. The exemplary system  200  may include the UE  110  in communication with a plurality of eNBs  220 - 240  of an LTE-RAN  210 . As described above, the UE  110  may also be capable of connecting to a legacy RAN. However, it is not necessary to illustrate the legacy RAN in  FIG. 2  because the exemplary cell reselection process is performed by the UE  110  to reconnect to the LTE-RAN  210 . 
     When the UE  110  is initially powered on, the UE  110  may be within the range of the plurality of eNBs  220 - 240 . In certain instances, the UE  110  may be surrounded by not only multiple eNBs from one network provider, but by multiple eNBs from multiple network providers. Out of those many eNBs, the UE  110  may only register, or camp, on one serving cell. Specifically, the UE  110  may perform a cell search procedure, wherein the cell scans and detects the available cells in the area. Throughout this description the terms “cell search,” “search,” “scan,” and their variants are used interchangeably to refer to a procedure for determining if a cell is available for connection by the UE  110  at a particular frequency. An “available” cell refers to a cell to which the network will allow the UE  110  to attach. There may be various parameters that are used to determine if the cell is available, e.g., the strength of the received signal at the UE  110 , the throughput or congestion of the cell, etc. 
     In order to determine which particular single cell for the UE  110  to register, the UE  110  goes through a specific decision making process called cell selection. During the cell selection process, the UE  110  observes various cell selection criteria, such as transmission power, signal strength, quality indicators, network type, service type, etc. Based on these criteria, the UE  110  will camp on one of the eNBs of the LTE-RAN  210 , e.g., eNB  220 . As described above, the UE  110  will exchange information (e.g., uplink (UL) and downlink (DL) communications) with the eNB  220  on a frequency within a frequency band that has been selected. Based on a variety of factors, this frequency/band combination may include the UE  110  operating in FDD mode or TDD mode based on the network providers traffic management scheme. 
     As noted above, the UE  110  is capable of using at least two network protocols, such as the LTE RAN for data connectivity and a legacy RAN for voice connectivity. Subsequent to the connection to the LTE-RAN  210 , the UE  110  may disconnect from the LTE-RAN  210  and connect to a legacy RAN to perform a voice call. Once the UE  110  completes the voice call on the legacy RAN, the UE  110  may then reconnect to the LTE-RAN  210 . This reconnection to the LTE-RAN  210  would typically require the UE  110  to re-perform the cell selection process described above. 
     However, since the UE  110  has previously connected with the LTE-RAN  210 , the exemplary embodiments modify the cell selection process to result in a cell reselection process that takes the previous connection to the LTE-RAN  210  into account when attempting to reconnect to the LTE-RAN  210 . Specifically, the cell reselection process considers and prioritizes the cell reselection process based on the frequency and/or band on which the UE  110  was previously communicating with the eNB  220  of the LTE-RAN  210 . In one exemplary embodiment, the UE  110  first prioritizes the cell reselection based on the previously used frequency. If the previously used frequency is not available, the UE  110  next prioritizes the cell reselection based on the previously used frequency band. 
     It should be apparent to those skilled in the art that this prioritization will make it more likely that the UE  110  will reconnect to one of the eNBs  220 - 240  of the LTE-RAN  210  using the same frequency or at least the same frequency band as was previously used, rather than just a strongest available frequency and/or band. Thus, if the UE  110  reconnects to the LTE-RAN  210  on the same frequency and/or band, it is more likely that the UE  110  will operate in the same mode (e.g., TDD or FDD) as was previously used by the UE  110  when connected to the LTE-RAN  210 . By reconnecting to the LTE-RAN  210  and operating in the same mode, the UE  110  is more likely to fit into the traffic management scheme desired by the network operator. 
     It should also be noted that the cell reselection process is not the initial cell selection process (e.g. when the UE  110  first joins the LTE-RAN  210  upon initial or subsequent power-up), but rather after the UE  110  has been previously connected to the LTE-RAN  210  without a power down. The exemplary cell reselection process may be used by the UE  110  for any reconnection to the LTE-RAN  210  subsequent to the initial cell selection process. The cell reselection process is performed subsequent to the initial cell selection process because the UE  110  uses information (e.g., frequency and/or band information) from previous connections to the LTE-RAN  210 . Upon the initial cell selection process, this information may not be available. 
       FIG. 3  shows an exemplary method  300  for a cell selection process (e.g., the initial cell selection process) by a mobile device, such as the UE  110 , in a wireless network, such as the LTE-RAN  210 , according to various embodiments described herein. As discussed above, the functions and operations of the UE  110  may be performed the exemplary processor  120 , as well as the various components of the UE  110 . 
     Initially, in  310 , the UE  110  may scan for all available cells, such as the plurality of eNBs  220 - 240 , in the area to establish contact with a public land mobile network (“PLMN”). Once a number of cells are detected, in  320 , the UE may perform PLMN selection to search for an available mobile network. Normally, the UE  110  utilizes its home PLMN, however a new PLMN may be selected if the home PLMN is unavailable. 
     Upon PLMN selection, in  330 , the UE  110  may use cell selection to determine which cell (e.g., eNB) to camp on and register its presence with the selected cell based on cell selection criteria. For instance, the UE  110  may create a candidate list of potential cells to camp on by using the cell selection process or, alternatively, stored cell selection information. During the cell selection process, the UE  110  scans all of the RF channels in the band to find a suitable serving cell. Typically, the UE  110  searches for the strongest cell on each network provider and reads its system information. Based on this information and the PLMN selection, the UE  110  is able to camp on the suitable cell (e.g., eNB  220 ). 
     In  340 , the UE may continue monitor the quality and measurements of signals of the serving cell as well as other cells within the area. Specifically, the E-UTRAN may control the quality measurements for the cells that are to be re-selected. The UE  110  measurements may be triggered based on threshold levels for serving cell quality measurements. In  350 , the UE  110  may discover a cell having stronger measurements than the serving cell in which the UE  110  is camped. Accordingly, in  360 , the UE  110  may select and camp on the neighboring cell (e.g., eNB  230 ) over the initial serving cell (e.g., eNB  230 ). It may be noted that under typical scenarios, the UE may continue to re-select and camp on the cell having the strongest measurements. 
     As described above, for the case where a network provider utilizes the eCSFB infrastructure, the UE  110  may receive data connectivity via the LTE-RAN  210  and voice and ancillary services are provided through an existing legacy RAN (e.g., 3G network such as CDMA2000, 1×RTT, 1×, etc.). Accordingly, the exemplary UE  110  may be connected to the LTE-RAN for data communications. Subsequently, when a user of the UE  110  initiates a mobile originated (“MO”) call or receives a mobile terminated (“MT”) call, the UE  110  may switch from LTE to CDMA. When the voice call ends, the UE  110  may return to the LTE-RAN  210  by performing a cell reselection process as described above. 
       FIG. 4  shows an exemplary method  400  for the UE  110  to perform a cell reselection process to reconnect with the LTE-RAN  210  based on prioritizing a previously used frequency and/or band by the UE  110 , according to various embodiments described herein. In describing the method  400 , it may be considered that the UE  110  is capable of communicating via two different protocols (e.g., LTE and CDMA). 
     In  405 , the exemplary UE  110  may initially associate and communicate with the LTE-RAN  210  via the eNB  220 . For example, the UE  110  may have performed the method  300  and selected and camped on the eNB  220 . As described above, when the UE  110  camps on the eNB  220 , the UE  110  communicates with the eNB  220  (e.g., transmit uplink information to and receive downlink information from) using a frequency within a frequency band. This frequency and frequency band will be termed the “camped frequency” and “camped band,” respectively. In  410 , the UE  110  may record both the camped frequency and the camped band with which it is communicating with the eNB  220 . 
     In  415 , the UE  110  may switch from the LTE-RAN  210  to the legacy RAN (e.g., CDMA). For instance, the UE  110  may receive or initiate a voice call. The MO or MT call may cause the UE  110  to disconnect from the LTE-RAN  210  and connect to the legacy RAN, such as a CDMA RAN for voice communications. 
     Upon the termination of the voice call over the legacy RAN, in  420 , the UE  110  may attempt to reconnect to the LTE-RAN  210 . In  425 , the UE  110  may determine whether or not the camped frequency recorded in  410  is available for reconnecting the UE  110  to LTE-RAN  210 . In other words, the highest priority attempt at reconnection is for the UE  110  to attempt to reconnect to the LTE-RAN on the last camped frequency. If the camped frequency is available, the method  400  may advance to  430  wherein the UE  110  may reconnect with the LTE-RAN  210  at the camped frequency. It should be noted that the UE  110  is likely to reconnect to the same eNB  220  to which the UE  110  was connected in  410 . However, it is also possible that the UE  110 , when connecting on the camped frequency, connects to one of the other eNBs  230  or  240  of the LTE-RAN  210 . Accordingly, regardless of which eNB  220 - 240  the UE  110  attaches to in the LTE-RAN  210 , the UE  110  may use the same frequency as the camped frequency in  405  and  430 . 
     If the camped frequency is not available, the method  400  may advance to  435 . In  435 , the UE  110  may perform a cell search within the camped band. In other words, if the camped frequency is not available to the UE  110 , the UE  110  may perform a narrowed cell search within the camped band recorded in  410 . In  440 , the UE  110  may determine whether or not a different frequency within the camped band recorded in  410  is available for use by the UE  110 . If a different frequency of the camped band is available, the method  400  may advance to  445  wherein the UE  110  reconnects with an eNB  220 - 240  of the LTE-RAN  210  using a frequency within the camped band. As noted above, the UE  110  does not necessarily reconnect to the same eNB  220  as it was connected to in  410 , and may connect to any eNB  220 - 240  using a frequency within the camped band in  410  and  445 . 
     If the camped band is not available, the method  300  may advance to  450 . In  450 , the UE  110  may perform a broader cell selection search beyond the camped band identified in  410 . For instance, the UE  110  may utilize the typical cell selection process as described in method  300 . 
     Accordingly, the exemplary method  400  provides the UE  110  with additional tasks to perform prior to simply executing a fresh cell search using a comprehensive band scan. The method  400  allows the UE  110  to prioritize its cell search procedure based on the last camped LTE frequency/band upon reconnection to the LTE-RAN  210  following the use of a legacy RAN (e.g., CDMA during a voice call). As detailed above, the UE  110  may first attempt to register on the last camped LTE frequency. If that frequency is not available, the UE  110  may then proceed to execute a cell search within the last camped LTE band. Thus, this method  400  may reduce the amount of time required by the UE  110  to reconnect to the LTE-RAN  210  (e.g., the “return to LTE” time). 
     Moreover, because the UE  110  will reconnect to one of the eNBs  220 - 240  of the LTE-RAN  210  using the same frequency or at least the same frequency band, it is more likely that the UE  110  will operate in the same mode (e.g., TDD or FDD) as was previously used by the UE  110  when connected to the LTE-RAN  210 . This means that upon reconnection with the LTE-RAN  210 , the UE  110  is less likely to degrade the network operator&#39;s traffic management schemes. 
     It may be noted that the exemplary embodiments are described with reference to the LTE wireless communication system. However, those skilled in the art will understand that the exemplary embodiments may be applied to managing the frequency selection of a mobile device within any wireless communication schemes including those having different characteristics from the LTE scheme. 
     It will be apparent to those skilled in the art that various modifications may be made in the present invention, without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

Metadata:
Filing Date: 20150529
Publication Date: 20170404
Grant Date: 20170404
Priority Date: 20150529
Inventors: BALAKRISHNAN SWAMINATHAN
VANGALA SARMA V.
VALLATH SREEVALSAN
SHARMA PRATEEK
Assignee: APPLE INC
CPC Classifications: [{"code": "H04W72/56", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04W48/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W72/0453", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W72/10", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04W48/18", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04W48/18", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W72/0453", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W48/14", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 57399518