Apparatus, systems and methods for initiating a cell selection

A device, system and method for initiating cell selection. The method is performed at a device connected to a network and camped on a first cell of the network. The method includes determining whether the device has successfully synchronized with the first cell. When the device is unable to synchronize with the first cell, the method includes determining whether at least one further cell satisfies predetermined reselection criteria and determining whether the at least one further cell satisfies initial cell selection criteria. When the at least one further cell satisfies the initial cell selection criteria, the method includes initiating an initial cell selection.

BACKGROUND

A user equipment (UE) may be configured to establish a connection to at least one of a plurality of different networks or types of networks to perform a variety of different functionalities via the network connection. To establish the connection, the UE may camp on a cell of a corresponding network. However, if the UE is unable to synchronize with the cell the UE is currently camped on, the UE may experience periods of no service or limited service where the UE cannot perform the full scope of functionalities normally available to the UE via the network connection.

Conventionally, while the UE is not exchanging data with the cell the UE is currently camped on (e.g. idle mode), the UE may perform measurements of the cells in the surrounding area. The UE may also be able to measure the connection between the UE and the cell the UE is currently camped on. Based on a comparison of these measurements to certain predetermined criteria, the UE may select a different cell to camp on. However, the UE may be unable to select a different cell to camp on if the predetermined criteria are not met.

Therefore, under conventional systems, the UE may remain camped on a cell that provides no service or limited service if the UE is unable to satisfy the criteria required to allow the UE to select a different cell to camp on. Accordingly, the following exemplary embodiments provide a solution for a UE to avoid being stuck on a cell that provides no service or limited service.

SUMMARY

The exemplary embodiments describe a method performed by a user equipment connected to a network and camped on a first cell. The method includes determining whether the user equipment has successfully synchronized with the first cell, determining whether at least one further cell satisfies predetermined cell reselection criteria and determining whether the at least one further cell satisfies initial cell selection criteria. Further, the method includes initiating initial cell selection when the UE has not successfully synchronized with the first cell and the at least one further cell satisfies the initial cell selection criteria.

According to another exemplary embodiment, a user equipment has a transceiver configured to establish a first connection with a first cell and a second connection with at least one further cell. The user equipment has a baseband processor connected to the transceiver configured to determine whether the user equipment has successfully synchronized with the first cell, determine whether the at least one further cell satisfies predetermined reselection criteria and determine whether the at least one further cell satisfies initial cell selection criteria. The user equipment has an application processor configured to cause the baseband processor to perform initial cell selection when the user equipment has not successfully synchronized with the first cell and the at least one further cell satisfies the initial cell selection criteria. The application processor causes the baseband processor to perform initial cell selection by deactivating the baseband processor then activating the baseband processor.

According to a further exemplary embodiment, an integrated circuit has circuitry to determine whether a user equipment has successfully synchronized with a first cell on which the user equipment is currently camped, circuitry to determine whether at least one further cell satisfies predetermined cell reselection criteria, circuitry to determine whether the at least one further cell satisfies initial cell selection criteria and circuitry to initiate initial cell selection when the user equipment has not successfully synchronized with the first cell and the at least one further cell satisfies the initial cell selection criteria.

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 a UE to perform cell selection and camp on an alternative cell when the UE is camped on a cell that provides either no service or limited service and the UE is unable to perform cell reselection. Specifically, the UE may be unable to synchronize with the cell the UE is currently camped on. Further, although the UE may determine that another cell may provide the UE with improved service, neither the characteristics corresponding to the connection between the UE and the cell the UE is currently camped on or the characteristics corresponding to a potential connection between the UE and an alternative cell satisfies the predetermined criteria required to trigger cell reselection. Thus, from a service perspective, the UE may be stuck camping on a cell that provides either no service or limited service. To connect with the cell that would provide the improved service the application processor of the UE may deactivate the baseband processor of the UE, then reactivate the baseband processor to allow the UE to perform cell selection and camp on the cell that provides the improved service. Accordingly, the exemplary embodiments described herein provide a mechanism for a UE to initiate cell selection when the UE is stuck camping on a cell that provides either no service or limited service.

Initially, it is noted that the exemplary embodiments are described with regard to a UE after the UE has been powered on and connected to a first network. Thus, the exemplary embodiments may relate to a UE that is currently camped on a first cell of a first network. The first cell of the first network merely refers to the cell the UE is currently camped on. It is not required that the first cell of the first network be the initial cell the UE camps on and the UE may have previously camped on a plurality of cells belonging to the first network or a plurality of cells belonging to different networks. In one example, the first network may be a Long Term Evolution (LTE) network. However, the UE may be currently camped on any type of network.

Further, the exemplary embodiments may be described with regard to the UE being unable to synchronize with the first cell of the first network. For example, in LTE, the UE may be unable to successfully utilize the random access channel (RACH) to synchronize with the first cell of the first network. Consequently, the UE may be unable to perform communication functionalities (e.g. receive calls). However the exemplary embodiments are not limited to a scenario where the UE is unable to synchronize with the cell that the UE is currently camped on and the exemplary embodiments may apply to a variety of other scenarios where the cell the UE is currently camped on provides either no service or limited service.

The exemplary embodiments may also relate to the UE being unable to initiate cell reselection. Cell reselection may refer to a mechanism that changes the cell the UE is camped on. For example, while a UE is camped on the first cell of the first network, the UE may determine measurement data corresponding to the connection between the UE and the first cell of the first network. The measurement data may be based on a single measurement, based on a plurality of measurements, derived from a measurement, derived from a plurality of measurements or based on a combination thereof. Subsequently, the UE may determine, based on the measurement data, to initiate cell reselection and attempt to camp on an alternative cell. For example, the UE may be triggered to initiate a cell reselection process and attempt to camp on an alternative cell if the measurement data fails to satisfy a predetermined threshold. An alternative cell may refer to a second cell of the first network or a first cell of a second network. It should be noted that the use of the terms “first cell”, “second cell”, “first network” and “second network” are merely for illustrative purposes and there may be a plurality of further cells for each respective network and there may be a plurality of further networks.

Alternatively, the cell reselection process may be based on measurements of other cells. For instance, when the UE is camped on the first cell of the first network the UE may determine reselection measurement data that may correspond to the quality of a potential connection between the UE and an alternative cell. Subsequently, the UE may initiate cell reselection and attempt to camp on an alternative cell based on the corresponding reselection measurement data. For example, the UE may be triggered initiate cell reselection and attempt to camp on an alternative cell if the measurement data satisfies a predetermined threshold. It should be noted that cell reselection may be initiated based on the measurement data corresponding to the connection between the UE and the first cell of the first network, the reselection measurement data corresponding to a potential connection between the UE and an alternative cell or a combination thereof. It should be further noted that reference to cell reselection is for illustrative purposes and other networks may refer to the process of connecting to different cells after the UE has initially camped on a particular cell in a different manner.

The exemplary embodiments described herein, provide a solution to the above noted deficiencies by initiating cell selection for a UE that may be stuck camping on a cell that provides either no service or limited service. Specifically, the UE may have determined that alternative cells can provide service and subsequently, the application processor of the UE may switch off the baseband processor of the UE to allow the UE to initiate cell selection. A person having ordinary skill in the art will understand that cell selection and cell reselection are different processes that may include different criteria. Specifically, cell selection is a process that takes place when the UE does not have a current connection to a network, e.g., when the baseband processor is powered cycled. Accordingly, by initiating cell selection, the UE may be able to camp on an alternative cell that provides service for the UE that allows the UE to be able to perform communication functionalities (e.g. receive calls).

FIG. 1shows an exemplary network arrangement100, according to various embodiments described herein. The exemplary network arrangement100includes a UE110. The UE110may be any type of electronic component that is configured to communicate via a network, e.g., smartphones, tablets, phablets, embedded devices, wearables, Internet of Things (IoT) devices, etc. It should also be understood that a network arrangement may include any number of UEs and the use of a single UE110is only provided for illustrative purposes.

In this example, each network is a wireless network with which the UE110may communicate wirelessly. However, it should be understood that the UE110may also communicate with other types of networks using a wired connection. Again, the use of two networks is only exemplary and there may be any other number of networks with which the UE110may communicate depending on the chipsets that are provided in the UE110. Thus, the UE110may be configured to communicate directly with one or more networks. In this example, the networks with which the UE110may communicate are a legacy radio access network (RAN)120and a Long Term Evolution (“LTE”) radio access network (LTE-RAN) network122. As will be described in detail below, the legacy RAN network120may refer to a plurality of different types of networks. Further, the LTE RAN network122and the legacy RAN network are considered different types of networks. Each of these different types of networks may be termed radio access technologies (“RATs”.)

LTE is defined as a standard for wireless communication of high-speed data for mobile phones and data terminals and has been described as a natural upgrade path for carriers using prior generation networks or legacy protocols, such as global System for Mobile Communications/Universal Mobile Telecommunications System (“GSM/UMTS”) protocols and Code Division Multiple Access (“CDMA”) 2000 1× (e.g., 1×RTT or simply “1×”) wireless communication protocols.

Legacy RAN120and the LTE-RAN122are portions of cellular networks that may be deployed by cellular providers (e.g., Verizon, AT&T, Sprint, T-Mobile, etc.). These networks120and122may include, for example, a plurality of cells or base stations (Node Bs, eNodeBs, HeNBs, etc.) that are configured to send and receive traffic from UEs that are equipped with the appropriate cellular chip set. Examples of the legacy RAN120may include those networks that are generally labeled as 2G and/or 3G networks and may include circuit switched voice calls and packet switched data operations. Each network may be a Public Land Mobile Network (PLMN). The PLMN is a regulatory term used in telecommunications representing a network established and operated by an administration or by a recognized operating agency for the specific purpose of providing land mobile telecommunications services to the public. The PLMN may include an operating area operating on a predetermined channel and utilizing a predetermined RAT (and/or band and/or channel). Once the UE has identified the available networks in the location that the UE is disposed, the UE may join a network in the given area by using a PLMN selection process.

As stated above, the legacy RAN120may include GSM or UMTS protocols and CDMA wireless communication protocols. It should be noted that UMTS may refer to Wide Band Code Division Multiple Access (WCDMA) wireless communication protocols and the term WCMDA may be used interchangeably with the term UMTS. Those skilled in the art will understand that the cellular providers may also deploy other types of networks, including further evolutions of the cellular standards, within their cellular networks (e.g. 5G networks).

The network arrangement100may also include a cellular core network130. The cellular core network130, the legacy RAN120and the LTE-RAN122may be considered a cellular network that is associated with a particular cellular provider (e.g., Verizon, AT&T, Sprint, T-Mobile, etc.). The cellular core network130may be considered to be the interconnected set of components that manages the operation and traffic of the cellular network. The interconnected components of the cellular core network130may include any number of components such as servers, switches, routers, etc.

FIG. 2shows an exemplary UE110according to various exemplary embodiments described herein. The UE110may be any electronic device that is configured to connect to a network and perform wireless functionalities. For example, the UE110may be a portable device such as a phone, a smartphone, a tablet, a phablet, a laptop, a wearable computing device, an Internet of Things (IoT) device, etc. In another example, the UE110may be a stationary device such as a desktop terminal.

The UE110may include an antenna (not shown) connected to a transceiver230that is connected to a baseband processor205. The baseband processor205may manage the radio functions of the UE110. The UE110further include an application processor210which may manage application processing for the UE110. Further, the application processor210may be able to activate and deactivate the baseband processor205. It should be noted that the application processor205may manage all the functions that are not managed by the baseband processor205. Alternatively, the UE110may include a plurality of further processors to manage other functions (e.g. display and power management). It should be further noted that while the exemplary UE110includes multiple processors a single processor may perform all of the functions of the individual processors and the use of a plurality of processors is merely for illustrative purposes. Additionally, a person having ordinary skill in the art would understand that any processor included in the UE110may be incorporated in, for example, an integrated circuit or chip.

The exemplary UE110may further include a display device220, an I/O device225and a memory arrangement215. Those skilled in the art will understand that the UE100may also include additional components235, for example, a Bluetooth transceiver, further input devices (e.g., a keypad, a touchscreen, etc.), a battery, etc. The memory arrangement215may be a hardware component configured to store data related to operations performed by the UE110. The display device220may be a hardware component configured to show data to a user while the I/O device225may be a hardware component that enables the user to enter inputs. It should be noted that the display device220and the I/O device225may be separate components or integrated together such as a touchscreen.

The transceiver230may be a hardware component configured to transmit and/or receive data. For example, the transceiver may be used to exchange data with cells (Node Bs, eNodeBs, HeNBs, etc.) that are configured to send and receive traffic from UEs that are equipped with the appropriate cellular chip set including the control information. Thus, the baseband processor205and the transceiver230may enable communication with a network, such as Legacy-RAN120and LTE-RAN122, as shown inFIG. 1, or with other electronic devices directly or indirectly through the particular network that the UE110is connected.

As mentioned above, the exemplary embodiments may relate to a UE that is unable to synchronize with the cell the UE is currently camped on and unable to initiate cell reselection.

The operating states of the UE110when it is camped on a cell of a network may be characterized as RRC idle state and RRC connected state. RRC refers to the radio resource control (RRC) protocols. Those skilled in the art will understand that when the UE110is in a RRC connected state, the UE110may be exchanging data with the connected network. For example, if the UE110is connected to the LTE-RAN122and in the RRC connected state, the UE110may exchange data associated with the connection that the UE110has established with the LTE-RAN122via a cell (e.g., an eNB) and thus the UE110is able to perform an operation that requires the exchange of data with the LTE-RAN122such as a communication functionality (e.g. receive calls). Further, those skilled in the art will understand that when the UE110is connected to the LTE-RAN122and in RRC idle state the UE110is operating in a low power state where the UE110is not exchanging data with the network and radio resources are not being assigned to the UE110within the network. However, when the UE110is operating in RRC idle state the UE110may listen to control channel broadcasts.

While the UE110is camped on a cell of a network the UE110may transition between the RRC operating states. For example, when the UE110is camped on a first cell of a first network in a RRC idle state, the UE110may not be able to exchange data with the network. To exchange data with the network the UE110may synchronize with the first cell of the first network and transition from RRC idle state to RRC connected state. Specifically, while in RRC idle state the UE110may listen to control channel broadcasts for information such as paging notifications of inbound traffic from the network. In response to the paging notification, the UE110may issue a request via the random access channel (RACH) to the network that indicates that the UE110wants to be moved to the RRC connected state. The successful transition of the UE110from RRC idle state to RRC connected state may include the exchange of messages between the UE110and the first cell of the first network. Once the transition to RRC connected state is complete, a network context is established between the first cell of the first network and the UE110. Thus, the UE110may be assigned radio resources and the UE110may be able to exchange data with the network.

It should be noted that the exemplary embodiments are not limited to only RRC connected state and RRC idle state. For example, when the UE110is operating within a WCDMA network, the RRC operating states may include an operating state that corresponds to the forward access channel (FACH). A UE110operating in a FACH state may be is similar to an RRC connected state, however, in this state the UE110utilizes shared channels to transmit information.

However, as mentioned above, the UE110may be unable to synchronize with the cell the UE110is currently camped on. For example, the UE110may not be able to synchronize with the cell the UE is currently camped on because the UE110may be unable to successfully complete the random access channel (RACH) procedure that may be required for synchronization. A person having ordinary skill in the art would understand that the RACH procedure includes a plurality of messages being exchanged between the UE110and the cell the UE110is currently camped on. The initial message in the RACH procedure is sent by the UE110to the cell the UE110is currently camped on via the RACH. The RACH is a shared medium utilized by the UEs within a network. The UE110may inform the network, via the RACH, that the UE110desires to connect to the network and camp on a particular cell within the network.

The RACH procedure is used to transition the UE110from RRC idle state to RRC connected state. The inability of the UE110to transition from RRC idle state to RRC connected state may be due to the RACH. Specifically, messages from different UEs using the RACH may collide because the RACH is a shared medium. The collisions may prevent requests by the UE110to the network regarding the UE110transitioning from the RRC idle state to the RRC connected state from being processed by the network. Thus, the UE110may be unable to synchronize with the cell the UE is currently camped on. Additionally, the UE110may also be unable to synchronize with the cell the UE110is currently camped on if the RACH cannot be successfully utilized to remedy scenarios such as when uplink data transfer synchronization is lost or when RRC connection reestablishment is required.

The scenarios described above pertaining to the RACH and the RACH procedure are merely for illustrative purposes and are not the only scenarios in which the UE may be unable to synchronize with the cell the UE is currently camped on. For instance, if a cell is operating within a WCDMA network the UE110may be unable to synchronize with a cell the UE is currently camped on due to the FACH being out of service. A FACH that is out of service may refer to a scenario where the cell the UE110is currently camped on does not meet a predetermined criteria and the UE110is unable to determine any alternative cell that may meet a predetermined criteria. Further, the inability of the UE110to synchronize with the cell the UE110is currently camped on may be based on a variety of other factors including issues corresponding to the connection between the UE110and the cell the UE110is currently camped on, issues corresponding to the protocol stack, interference from other types of connections (e.g. WiFi, Bluetooth, etc.) or anything else that prevents the UE110from being able to synchronize with the cell the UE110is currently camped on. It should also be noted that the exemplary embodiments are not limited to synchronization and may apply to any scenario where the UE110is currently camped on a cell that provides either no service or limited service.

The exemplary embodiments may also relate to the UE110being unable to initiate cell reselection. Cell reselection refers to a mechanism where the cell the UE110is camped on is changed. For example, the mechanism may change the UE110from being camped on the first cell of the first network to being camped on a second cell of the first network or a first cell of a second network.

Cell reselection may be triggered based on measurements or indications regarding the quality of the connection between the UE110and the first cell of the first network. Further, cell reselection may also be triggered based on reselection measurements corresponding to alternative cells belonging either to the first network or an alternative network. Thus, the UE110may attempt to initiate cell reselection if the measurements or indications regarding the quality of the connection between the UE110and the first cell of the first network do not satisfy a predetermined criteria or if reselection measurements corresponding to alternative cells do not satisfy a predetermined criteria. It should be noted that the UE110may perform these reselection measurements while the UE110is operating in a RRC idle state.

The UE110may be unable to initiate cell reselection even when the UE110is camped on a cell that provides either no service or limited service. Specifically, the UE110may be unable to initiate cell reselection if the measurements corresponding to the cell the UE110is currently camped on do not meet a certain predetermined criteria. Additionally, the UE110may be unable to initiate cell reselection if the measurements corresponding to alternative cells do no meet a certain predetermined criteria. Further, the UE110may be unable to perform cell reselection when there is an imbalance between the downlink and uplink connection. For example, an imbalance may occur when the downlink connection between the UE110and the cell the UE110is currently camped on is being used to send data to the UE110but there are issues with the uplink connection and the UE110cannot use the uplink connection to reliably send data to the network. Thus, the imbalance may prevent the UE110from being able to perform voice operations. However, the imbalance may cause the UE110to determine that cell reselection is not necessary because the downlink is working properly. The exemplary embodiments are not limited to a UE110that is unable to perform cell reselection and the exemplary embodiments may apply to any scenario that prevents the UE110from being able to initiate a process that allows the UE110to camp on an alternative cell.

The exemplary embodiments described herein may utilize information that corresponds to cell selection. Cell selection refers to the selection of the initial cell the UE110camps on after the UE110has been powered on. Cell selection may relate to a scenario where the UE110is surrounded by a plurality of cells. The UE110may only select one cell to camp on. Therefore, cell selection relates to a process of differentiating, based on predetermined criteria, between the cells surrounding the UE110to select a cell that the UE110may camp on.

It should be noted that cell selection may include decoding master information blocks (MIBs) and decoding system information blocks (SIBs) that are transmitted by the cells. A person having ordinary skill in the art will understand the quantity and type of information contained in MIBs and SIBs.

FIG. 3shows a method300for the UE110to perform cell selection according to various embodiments described herein. The method300relates to how the UE110initiates cell selection when the UE110is unable to perform cell reselection and camped on a cell that provides either no service or limited service. The method300will be described with regard to the network arrangement100ofFIG. 1and the UE110ofFIG. 2.

In305, it may be considered that the UE110may be currently connected to a LTE network and camped on an eNB (e.g. eNB122B) and the UE110attempts to synchronize with the eNB122B. For example, the UE110may want to use the RACH to transition from a RRC idle state to a RRC connected state or the UE110may wish to remedy the loss of uplink synchronization. If synchronization was successful then data and voice services are available and the method300is completed. However, if synchronization was unsuccessful, the method300continues to310. It should be noted that synchronization may refer to any failure that results in the UE110being camped on a cell that provides either no service or limited service, including, but not limited to the failures that were described above.

In310, the UE110determines if an alternative cell within the LTE network (e.g. eNB122A) or an alternative cell within the legacy network (e.g. NodeB120A) may provide service that exceeds the quality of the service being provided by the eNB122B (e.g., no service or limited service). To make this determination the UE110may perform measurements that correspond to the characteristics of a potential connection between the UE110and the alternative cell. For example, the UE110may determine if the alternative cell is transmitting a signal with adequate signal strength to be recognized by the UE110.

Alternatively, the UE110may utilize the criteria the UE110utilizes for initial cell selection to determine if an alternative cell may provide service that exceeds the currently camped on cell. As stated above, cell selection and cell reselection are different processes and are not analogous. The criteria for cell selection may be less than cell reselection criteria and may include, but is not limited to, characteristics that correspond to signal strength of the respective cell, characteristics that correspond to signal quality offered by the respective cell, whether the PLMN of the cell is a PLMN the UE110is permitted to utilize, whether the service offered by the cell is a type of service the UE110is permitted to utilize, etc. An example of a specific measure that may be determined during cell selection is the minimum required reception level in the cell (Qrxlevmin). Further, as stated above, cell selection may include decoding SIBs and deriving system information. However, cell selection is not limited to the criteria discussed above and different networks may utilize different criteria.

One exemplary embodiment the UE110may utilize for initial cell selection to determine if an alternative cell may provide service that exceeds the currently camped on cell may include storing the system information for a corresponding cell when the UE110is determining whether a cell is suitable for initial cell selection. The UE110may determine the system information by decoding SIBs or performing measurements. The UE110may store the system information for only the cells that were evaluated during the most recent initial cell selection process or the UE110may store the system information for cells that were evaluated over a plurality of initial cell selection processes. Specific system information that may be stored may include the Qrxlevmin, the physical cell identity and the E-UTRA Absolute Radio Frequency Channel Number (EARFCN). The EARFCN identifies the LTE band and carrier frequency of the corresponding cell. However, the exemplary embodiments are not limited to these types of system information and the UE110may store any other type of system information that corresponds to initial cell selection. The UE110may use the stored system information of the respective cells to determine if any of the cells may provide service that exceeds the currently camped on cell and thus, the UE110may make this determination faster than if the UE110had to actively determine if any of the alternative cells may provide service that exceeds the currently camped on cell without using stored system information.

Another exemplary embodiment may utilize the Access Stratum (AS) to determine if an alternative cell may provide service that exceeds the currently camped on cell. The AS corresponds to plurality of protocols. For example, one AS protocol may correspond to a neighbor cell search, which is the procedure for which the UE110acquires time and frequency synchronization with a cell and detects the cell ID of that cell. Specifically, information pertaining to neighbor cells may be provided in data received in the downlink connection as part of the AS protocol. The UE110may utilize the information corresponding to the AS protocol to determine if an alternative cell may provide service that exceeds the currently camped on cell. Further, the UE110may evaluate information corresponding to the AS protocol against the stored system information described above or against another predetermined threshold to determine if an alternative cell may provide service that exceeds the currently camped on cell.

If, in310, the UE110determines that an alternative cell may provide service that exceeds the currently camped on cell the method300may continue to315. The UE110may make this determination using any of the factors or criteria described above, individually or in combination.

In315, the UE110determines if there are any cell reselection candidates. Again, as stated above, cell selection and cell reselection are different processes and are not analogous. Cell reselection criteria may exceed cell selection criteria. Here, if the UE110determines that there are no cell reselection candidates available the method300continues to320. For example, a UE110may determine that there are no cell reselection candidates based on measurement data corresponding to the connection between the UE110and the cell the UE110is currently camped on or the reselection measurement data corresponding to alternative cells fails to meet a predetermined criteria. However, the method300is not limited to evaluating measurement data or reselection measurement data and the UE110may determine whether there is any reselection candidates based on any available information.

In320, the UE110determines whether data and/or voice service has been unavailable for a predetermined duration. The predetermined duration may correspond to a single failure for the UE110to synchronize with the cell the UE110is currently camped on or the predetermined duration may correspond to a plurality of failures to synchronize with the cell the UE110is currently camped on. Alternatively, the UE110may set the predetermined duration to any length of time. If the service has been unavailable for the predetermined duration the method300continues to325.

In325, the UE110initiates airplane mode where the application processor210of the UE110deactivates the baseband processor205of the UE110. By initiating airplane mode and deactivating the baseband processor205of the UE110, the UE110will no longer be camped on the network. Subsequently, the UE110deactivates airplane mode which activates the baseband processor205. Coming out of airplane mode allows the UE110to perform cell selection and select the best available service based on information stored in the memory of the UE110. It should be noted that the exemplary embodiments are not limited to airplane mode and may refer to any process of deactivating and activating the baseband processor205to perform cell selection. The use of airplane mode allows the UE110to initiate cell selection and camp on an alternative cell that the UE110had previously determined would provide service that exceeds the currently camped on cell. The UE110may prioritize the order of the alternative cells in which the UE110may attempt to camp on based on the information determined in310.

In330, the UE110successfully completes the cell selection process initiated in325. Accordingly, data and/or voice service may be available to UE110and the UE110is no longer stuck camping on a cell that provides no service or limited service.

As discussed above, the exemplary embodiments are not limited to scenarios where the UE110is currently camped on a cell that belongs to a LTE network. For example, the UE110may be camped on a cell that belongs to a legacy network. Specifically, the UE110may be currently camped on a cell that belongs to a WCDMA network.

When a UE110is currently camped on a cell that belongs to a WCDMA network the UE110may be unable to synchronize with the cell the UE110is currently camped on. The inability of the UE110being unable to synchronize with the cell may be due to the FACH being out of service. A FACH that is out of service may refer to a scenario where the cell the UE110is currently camped on does not meet certain criteria and the UE110is unable to determine any alternative cell that meets a certain criteria. However, it should be noted that synchronization issues that occur when a UE110is currently camped on a WCDMA cell is not limited to the issues corresponding to the FACH and a variety of other issue may occur with the other channels used within a WCDMA network that may result in a UE110being unable to synchronize with the cell the UE110is currently camped on. For example, when the UE110is utilizing FACH the UE110may still be utilizing the RACH and the UE110may be unable to synchronize with the cell the UE110is currently camped on due to an issue associated with the RACH.

Further, considering a scenario when the FACH is out of service, if the UE110suddenly loses a cell when the UE110is attempting to perform a cell update procedure, the AS attempts to perform a recovery search to transition the cell to a different operating state. However, the UE110is not synchronized with the cell the UE110is currently camped on, the UE110no longer has a target cell and there are no alternative cells to camp on as demonstrated by the FACH being out of service. A cell update procedure may correspond to a UE110from being camped on a particular cell to being camped on a alternative cell. Thus, in this scenario, the UE110may be stuck camping on a cell that provides no service or limited service and the UE is unable to perform cell reselection. It should be noted that the above scenario is merely for illustrative purposes and there may be a variety of other factors within a WCDMA network where the UE110may be stuck camping on a cell that provides no service or limited service and the UE is unable to perform cell reselection.

To solve the above noted deficiencies, the UE110may utilize non-access stratum (NAS) selection to trigger cell selection. NAS is part of the protocol stack. The NAS may function in RRC idle mode and perform tasks associated with PLMN selection and cell selection. For example, the NAS may maintain a list of PLMNs in priority order and evaluate reports of available PLMNs from the AS for PLMN selection. The NAS may control cell selection by indicating the RATs associated with the selected PLMN to be used in the search of a cell in the cell selection process. A person having ordinary skill in the art will understand that the NAS is not limited to functions associated with PLMN selection or cell selection and the NAS may perform a variety of other functions. The use of NAS selection to trigger initial cell selection when the UE110may be stuck camping on a cell that provides no service or limited service and the UE is unable to perform cell reselection prevents the protocol stack from being completely torn down and allows the UE110to find an alternative cell to camp on in a faster and more power efficient manner.

FIG. 4shows a method400for the UE110to perform NAS selection according to various embodiments described herein. The method400relates to how the UE110initiates NAS selection when the UE110is camped on a cell that provides no service or limited service and is unable to perform cell reselection. It should be noted that the method400may be described with the UE110initially being camped on a WCDMA cell. However, the method400does not require the UE110to be camped on a WCDMA cell and the UE110may be camped on any type of cell (e.g. LTE cell). Further, the method400will be described with regard to the network arrangement100ofFIG. 1and the UE110ofFIG. 2.

In405, the UE110may be stuck camping on a cell that provides no service or limited service because the UE is unable to perform cell reselection. For example, the UE110may be camping on a WCDMA cell. The UE110may be stuck camping on a cell due to the UE110being unable to synchronize with the cell the UE110is currently camped on as a result of the FACH being out of service or an issue associated with the RACH. It should be noted that the use of a WCDMA cell is merely for illustrative purposes and the UE110may be stuck camping on any type of cell.

In410, the UE110may determine whether there are any cells that may provide service that exceeds the currently camped on cell.410is similar to310and the UE110may make this determination using any of the factors or criteria described above with regard to310, individually or in combination. In410, if the UE110determines that there are alternative cells that may provide service that exceeds the currently camped on cell the method400continues to415.

In415, the UE110triggers NAS selection. The NAS selection may be triggered after a predetermined number of RACH failures or a predetermined amount of time. Further, based on the determination made in410the UE110may determine a priority order of cells with which to attempt NAS selection and the UE110may give the highest priority to LTE cells. For example, the UE110may be stuck camping on a WCDMA cell and perform NAS selection on a LTE cell based on the priority given to the LTE cell. However, even if a UE110is stuck camping on a LTE cell the UE110may perform NAS level selection on an alternative LTE cell.

One exemplary embodiment of NAS selection may provide more efficient NAS selection by placing a maximum amount of attempts on the NAS attempt counter. The NAS attempt counter is used to limit that amount of rejected NAS selection attempts. The maximum may be based on the determination made in410. Thus, the maximum amount of attempts may correspond to the quantity or quality of alternative cells the UE110has determined may provide service that exceeds the currently camped on cell. For example, the more alternative cells that provide suitable connections for the UE110the lower the maximum number of NAS selection attempts may be set because if the UE110is unable to camp on a first potentially suitable cell via NAs selection the UE110knows that there is still another potential NAS selection eligible cell available.

Another exemplary embodiment of NAS selection may provide more efficient NAS selection by triggering NAS selection immediately upon N300 counter expiry. The N300 represents the maximum number of RRC connection request retransmits and may be set to any value from 0 to 7.

Another exemplary embodiment of NAS selection may provide more efficient NAS selection by triggering NAS selection when the downlink block error rate (BLER) corresponding to the cell the UE is currently camped on is less than the predetermined threshold and the transmission power for the cell the UE is currently camped on is greater than or equal to the maximum transmission power level (MTPL) for a predetermined number of RACH attempts.

Another exemplary embodiment of NAS selection may provide more efficient NAS selection by triggering NAS selection based on a RACH attempt counter that is adjusted dynamically. The RACH attempt counter may be adjusted based on a number of RACH preambles transmitted, the T300 times and the N300 counter. A person having ordinary skill in the art will understand that the amount of RACH preambles transmitted corresponds to the number of RACH attempts because a RACH procedure includes initially transmitting a RACH preamble.

It should be noted that in415, the UE110may trigger NAS selection to allow the UE110to camp on an alternative cell based on a single factor described above or a combination thereof.

In420, the UE110may successfully complete the NAS selection and thus, the UE110successfully camps on an alternative cell. Accordingly, service to the UE110is restored.

The described exemplary embodiments may be implemented in any suitable software or hardware configuration or combination thereof. An exemplary hardware platform for implementing the exemplary embodiments may include, for example, an Intel x86 based platform with compatible operating system, a Mac platform and MAC OS X, mobile platforms having operating systems such as iOS. Android, etc. In a further example, the exemplary embodiments of the above described method may be embodied as a program containing lines of code stored on a non-transitory computer readable storage medium that, when compiled, may be executed on a processor or microprocessor.

It will be apparent to those skilled in the art that various modifications may be made in the present embodiments, without departing from the spirit or the scope of the exemplary embodiments. Thus, it is intended that the exemplary embodiments cover modifications and variations provided they come within the scope of the appended claims and their equivalent. It will also be understood that the T300 timer correspond to the amount of time between the transmissions of RRC connection requests.

It is further noted that the exemplary embodiments are described with a set of conditions that are determined for the mechanism according to the exemplary embodiments to be performed. However, the set of conditions described herein are only exemplary and the set of conditions may include further criteria or omit certain criteria as used herein. Thus, the set of conditions described herein are only exemplary and those skilled in the art will understand that other conditions or sets of conditions may be utilized when a substantially similar mechanism according to the exemplary embodiments would provide the features described herein.