METHOD TO PRIORITIZE 5G NSA CELL (RE) SELECTION, AND COMPUTER SYSTEM

During the transition period from 4G and long-term evolution (LTE) to 5G technology, for 5G capable user equipment (UE), it is preferred to utilize non-standalone (NSA) cells that support 5G technology rather than LTE only cells. To enable such preference, a fingerprint database recording known neighboring NSA cells to LTE only cells and a flag for identifying NSA cells in the acquisition database of the UE can be used to prioritize searching for NSA cells on startup and to expedite reselection to an NSA cell when camping on LTE only cells. To avoid excess battery drain when camping on LTE only cells since searching for cells consumes significant power of the UE, a series of timers and a counter can be used to disable the NSA preferred feature if an NSA cell is not found after a reasonable search while camping on the LTE only cell.

TECHNICAL FIELD

Aspects of the disclosure relate to communications telephony and more particularly to a method to prioritize 5G non-standalone (NSA) cell (re)selection, and a computer system.

BACKGROUND

Changing technology in wireless communication is leading to a change from 4th Generation (4G) and Long-term evolution (LTE) technology to 5thGeneration (5G) technology. The current infrastructure (e.g., cellular towers) support LTE communication. As the change to 5G technology arrives, the infrastructure is slowly changing to a hybrid LTE/5G stage. During this hybrid stage, LTE only cells (legacy LTE cells that do not support 5G) remain, and NSA cells (LTE cells which have a 5G neighbor cell) are also available for supporting communication on the network. During this transition period LTE only and NSA cells, there is currently no preference for 5G capable user equipment (UE) to use NSA cells rather than LTE only cells. Accordingly, the 5G capable UE may not take advantage of the faster speed available with 5G communication.

SUMMARY

One general aspect includes a method of preferably accessing non-standalone (NSA) cells during startup of user equipment (UE). In such methods, the UE may search an acquisition database for an entry marked with an NSA flag indicating the associated entry is for an NSA cell. If an NSA cell that meets cell selection criteria is found in the acquisition database, the UE camps on the NSA cell. If no NSA cell is found in the acquisition database or it does not meet the cell selection criteria, the UE searches the acquisition database for other entries marked with a false value for the NSA flag indicating the associated entry is for a long-term evolution (LTE) only cell. The UE may camp on the LTE only cell if the LTE only cell is found in the acquisition database and meets the cell selection criteria. If no LTE only cell is found in the acquisition database or the LTE only cell does not meet the cell selection criteria, the UE may execute a band scan. The UE may camp on the NSA cell to avoid repeated reselection to multiple LTE only cells in short succession. Other embodiments of this aspect include corresponding computer systems, apparatus, and computer programs recorded on one or more computer storage devices, each configured to perform the actions of the methods.

Implementations of the above method may include one or more of the following features. In at least one implementation, the acquisition database has a number of entries reserved for NSA cells. In at least one implementation, the band scan includes scanning frequencies for a cell that meets the cell selection criteria without scanning frequencies scanned from the acquisition database a second time. In at least one implementation, the UE may update a fingerprint database with the frequency and cell identifier of the NSA cell the UE camps on. Implementations of the described techniques may include hardware, a method or process, or computer software on a computer-accessible medium.

Another general aspect includes a method for a user equipment (UE) to identify a non-standalone (NSA) cell while camping on a long-term evolution (LTE) only cell. In such methods, the UE may search a fingerprint database for a discovered neighbor NSA cell associated with the LTE only cell. If the UE finds an NSA cell listed as a discovered neighbor NSA cell in the fingerprint database, the UE may measure the frequency associated with the discovered neighbor NSA cell for reselection. If the UE does not find a discovered neighbor NSA cell in the fingerprint database or the discovered neighbor NSA cell does not meet the reselection criteria, the UE may execute an NSA background search. Other embodiments of this aspect include corresponding computer systems, apparatus, and computer programs recorded on one or more computer storage devices, each configured to perform the actions of the methods.

Implementations of the above method may include one or more of the following features. In at least one implementation, the UE may execute a first timer. In at least one implementation, the NSA background search includes, upon expiration of the first timer, the UE searches an acquisition database for an NSA cell that meets the reselection criteria. If the UE finds an NSA cell in the acquisition database, the UE measures the frequency associated with the NSA cell for reselection. If the UE does not find an NSA cell in the acquisition database or the NSA cell does not meet the reselection criteria, the UE searches the neighbor NSA cell frequency list for a neighbor NSA cell that meets the reselection criteria. If the UE finds a neighbor NSA cell in the neighbor NSA cell frequency list, the UE measures the frequency associated with the neighbor NSA cell for reselection. If the UE does not find a neighbor NSA cell or the neighbor NSA cell does not meet the reselection criteria, the UE may execute a band scan. In at least one implementation, the UE may increment a counter if no NSA cell that meets the reselection criteria was identified during the NSA background search. The UE may execute a second timer if the counter is less than a threshold value. Upon expiration of the second timer, the UE may re-execute the NSA background search.

In at least one implementation, the band scan includes searching for a derived NSA cell from the acquisition database. If the UE is able to derive an NSA cell from the acquisition database, the UE may measure the frequency associated with the derived NSA cell for reselection. If the UE cannot derive an NSA cell from the acquisition database or the NSA cell does not meet the reselection criteria, the UE may search a priority band list for a priority NSA cell. If the UE finds a priority NSA cell in the priority band list, the UE measures the frequency associated with the priority NSA cell for reselection. If the UE does not find a priority NSA cell in the priority band list or the priority NSA cell does not meet the reselection criteria, the UE may scan all remaining frequency bands to find an NSA cell suitable for camping on. At any time an NSA cell is identified that meets the reselection criteria, the UE may camp on the NSA cell and stop searching. In at least one implementation, in response to determining the UE is camped on an LTE only cell, the UE may temporally increase all NSA cell reselection priority, rank all NSA cells based on signal quality or signal strength, and select the highest ranking NSA cell. The UE may evaluate the highest ranking NSA cell using the reselection criteria to expedite reselecting an NSA cell over remaining on the LTE only cell. In at least one implementation, in response to determining the UE is camped on an NSA cell, the UE may temporally increase a high priority threshold for a high priority LTE only neighbor cell and temporally increase an offset for intra frequency/equal priority inter frequency for neighbor LTE only cells to keep the UE from reselecting to a LTE only cell over the NSA cell it is camped on. Implementations of the described techniques may include hardware, a method or process, or computer software on a computer-accessible medium.

Yet another general aspect includes one or more processors; one or more memories storing computer-readable instructions that, upon execution by the one or more processors, configure the computer system to: search an acquisition database for an entry marked with a first value for a non-standalone (NSA) flag indicating the associated entry is for an NSA cell; camp on the NSA cell associated with the entry based upon a determination that the NSA cell meets a cell selection criteria; search the acquisition database for a second entry marked with a second value for the NSA flag indicating the associated entry is for a long-term evolution (LTE) only cell based upon a determination that the NSA cell does not meet the cell selection criteria; camp on the LTE only cell associated with the second entry based upon a determination that the LTE only cell meets the cell selection criteria; execute a band scan based upon a determination that the LTE only cell does not meet the cell selection criteria.

In at least one implementation, the acquisition database has a number of entries reserved for a plurality of NSA cells.

In at least one implementation, the band scan comprises scanning a plurality of frequencies for a cell that meets the cell selection criteria.

In at least one implementation, frequencies scanned from the acquisition database are not scanned again.

In at least one implementation, the computer-readable instructions that, upon execution by the one or more processors, are operable with the computer system to: in response to camping on the NSA cell associated with the entry, update a fingerprint database with a frequency and cell identifier of the NSA cell and any neighboring LTE only cells.

In at least one implementation, the acquisition database comprises, for each entry, a cell identifier, a frequency, and a value for the NSA flag.

In at least one implementation, the computer-readable instructions, upon execution by the one or more processors, are operable with the computer system to further stops searching and configures settings to remain camped on the NSA cell after be camped on the NSA cell.

DETAILED DESCRIPTION

Embodiments of the present disclosure are directed to, among other things, preferably selecting an NSA cell over an LTE only cell upon startup of the UE. During the transition period between LTE and 5G technologies, legacy cells that are LTE only cells (i.e., does not support 5G) may remain and NSA cells (i.e., LTE cells with a 5G neighbor cell) are included in the communication network. NSA cells allow the network to add the UE to the neighboring 5G cell to use the 5G service. Therefore, for 5G capable UEs, it is preferable for the UE to select an NSA cell as the serving cell (i.e., to camp on). The UE can prioritize the scan for a serving cell to scan for NSA cells first, if known, by searching an acquisition database containing previous serving cells of the UE for cells that are marked as NSA cells. To expedite finding service on startup, if no NSA cells are found in the acquisition database that are suitable, the UE can find an LTE only cell in the acquisition database to camp on.

Additionally, embodiments are directed to expediting reselection of a serving cell for a UE that is camped on an LTE only cell to search for an available NSA cell. Otherwise, 5G capable UEs may be stuck on LTE only cells, unable to utilize the faster 5G service. The UE may utilize timers and a counter to periodically search for an NSA cell efficiently to avoid battery drain since searching for cells is a power consuming activity of the UE. The UE searches for a suitable NSA cell starting with known potential NSA cell frequencies based on the serving LTE only cell. If an NSA cell is found, the UE will use the reselection process to reselect to the NSA cell as the serving cell. If no suitable NSA cell is located, the search is repeated after a period of time. To avoid excessive batter drain, the process of searching for an NSA cell is stopped after the search is executed a number of times, checked using a counter each time the search is executed.

Additionally, once the UE is camped on an NSA cell, the searching process is discouraged by setting threshold values that encourage the UE to remain on the NSA serving cell. Otherwise, the UE may jump to an LTE only cell because the connection is stronger.

FIG. 1illustrates an example communication system100. The communication system100includes user equipment (UE)105, long-term evolution (LTE) only cell110, non-standalone (NSA) cell115, and 5G cell120. While described with only a single UE105, LTE only cell110, NSA cell115, and 5G cell120, communication system100may include any number of each component.

LTE only cell110may be any cellular communication tower that supports LTE cellular technology but does not have a neighboring 5G cell120. Without a neighboring 5G cell120, the LTE only cell110cannot allow the network to add the UE105to the 5G cell120when the UE105is camped on the LTE only cell110(i.e., the LTE only cell110is the serving cell for the UE105).

NSA cell115may be any cellular communication tower that supports LTE cellular technology and has a neighboring 5G cell120. When UE105is camped on the NSA cell115, the NSA cell115can allow the network to add the UE105to the 5G cell120.

5G cell120may be any cellular communication tower that supports 5G cellular technology. 5G cell120may be smaller than LTE only cell110and NSA cell115. In current communication networks and UEs105, the UE105can utilize the 5G cell120by connecting to the NSA cell115as the serving cell, which can allow the network to add the UE105to the 5G cell120.

User equipment (UE)105may be any suitable mobile device that has wireless communication ability for accessing an LTE network and that supports 5G technology. UE105includes memory140, application processor130, and modem135. UE105may include additional components left out ofFIG. 1for ease of description such as, for example, a display, a user interface, and the like. UE105may include, for example, components described in computer system1000as described with respect toFIG. 10.

Application processor130may be a chip used for the primary application processing in UE105. For example, the application processor130may execute instructions in memory140, including, for example, the instructions included in startup subsystem145, and reselection subsystem165. A different chip may handle, for example, the display of the UE.

Modem135may be a chip used to enable communication on the network using LTE or 5G technology (e.g., communication protocols and the like). Modem may allow UE105to communicate with LTE only cell110, NSA cell115, and/or 5G cell120. The modem may have some processing capability including the ability to set values in memory140and may communicate with the application processor130to provide data received from LTE only cell110, NSA cell115, and/or 5G cell120.

Memory140includes acquisition database155, fingerprint database160, timers150, reselection subsystem165, and startup subsystem145. Memory140may include additional components not described herein for simplicity, and the functionality described herein may be incorporated into more or fewer components of memory140without departing from the scope of this disclosure.

Acquisition database155may be a database including information on each cell that UE105has previously camped on (i.e., each cell that has been a serving cell for UE105). The acquisition database155can include an entry for each cell. The acquisition database155may include, for example, the public land mobile network (PLMN) identifier for the cell, the cell identifier of the cell, the frequency for the cell, and a flag value indicating whether the cell is an NSA cell or not. The information for the known cells stored in the acquisition database155can be used to more quickly identify a suitable serving cell for the UE105on startup, and the flag value can be used to give preference to the NSA cell115. Further, the acquisition database155can be used to identify preferable NSA cells115during reselection if the UE105is camped on LTE only cell110. An example acquisition database155is depicted and described with respect toFIG. 2.

Fingerprint database160may be a database including information about known LTE only cells110and corresponding neighboring NSA cells115. UE105may or may not have used LTE only cells110and/or NSA cells115as serving cells for their entry in fingerprint database160. Rather, when UE105receives information about a neighboring LTE only cell110to NSA cell115that UE105is camped on, or when UE105receives information about a neighboring NSA cell115to LTE only cell110that UE105is camped on, UE105may update the fingerprint database160to include such information. Fingerprint database160may be used to expedite cell reselection from an LTE only cell110to an NSA cell115. An example fingerprint database160is depicted and described with respect toFIG. 3.

Timers150may include at least two timers and a counter. The timers and counter are used during the preferred NSA background search575as described with respect toFIG. 5. The first timer is a shorter timer of, for example, 5 seconds that is used after determining the UE105is camped on LTE only cell110. After expiration of timer1, the preferred NSA background search575is performed, which includes the counter and timer2. After the preferred NSA background search575completes, the counter is incremented and compared against a threshold value. If the counter is less than the threshold, timer2is executed, and the preferred NSA background search575is completed again. The timers and counter help ensure that the battery of the UE105is not consumed by unnecessary searching, which is a power consuming task. If a suitable NSA cell115is not found during the preferred NSA background search575after the threshold number of attempts, the application processor130or the modem135disable the 5G NSA preferred mode functionality. For example, the counter and two timers are reset and a flag may be set indicating the preferred NSA functionality is off. When the preferred NSA functionality is disabled, legacy search and selection behavior resumes, which does not prioritize NSA cell selection.

Startup subsystem145may include instructions that are utilized when the UE105starts up and begins searching for service. The instructions prioritize finding a NSA cell115to camp on based on known information in the acquisition database155including the flag indicating whether the cell is an NSA cell115. If an NSA cell115that meets selection criteria is not found in the acquisition database155, an LTE only cell110can be selected from the acquisition database155that meets the selection criteria. If no cell within acquisition database155is found that meets the selection criteria, a band scan is executed to find a cell that meets the selection criteria. The band scan continues until the UE finds a suitable serving cell. Flowchart400described with respect toFIG. 4illustrates the startup process performed by startup subsystem145.

Reselection subsystem165may include instructions that are utilized when UE105is camped on LTE only cell110that prioritize reselection of an NSA cell115. To ensure that UE105has service, if NSA cell115is not found quickly, UE105selects LTE only cell110as the serving cell. Once on an LTE only cell110, UE105may expedite preferential searching for NSA cell115to reselect and use as the serving cell. The fingerprint database160is searched for NSA cell115, and if fingerprint database160does not have an entry for NSA cell115, UE105performs an ordered search to identify a preferred NSA cell115to camp on. Flowchart500described with respect toFIG. 5illustrates the reselection process performed by reselection subsystem165.

FIG. 2illustrates an example legacy acquisition database205without an NSA cell flag210and a second example acquisition database155with NSA cell flag210. The data shown in legacy acquisition database205and acquisition database155is for exemplary purposes and does not limit the scope of the description.

Legacy acquisition database205does not include NSA cell flag210and has fewer entries than acquisition database155as it may be limited to fewer entries than acquisition database155. Legacy acquisition database155may not be used for the described 5G NSA preferred mode described herein. Rather, legacy acquisition database155may be used for UEs105that do not have 5G capability or otherwise do not implement the 5G NSA preferred mode.

Acquisition database155may include the same information as legacy acquisition database205, but further may include the NSA cell flag210value for each entry. Acquisition database155may also have more entries than legacy acquisition database205. Each entry may include, for example, an entry number, a public land mobile network (PLMN) identifier for the cell, a frequency for the cell, a cell identifier for the cell, and an NSA flag210value for the cell. In some embodiments, the cell identifier combined with the frequency for the cell creates a unique combination for each cell. In some embodiments, the NSA cell flag210is a binary value that is set to TRUE (e.g.,1) or FALSE (e.g.,0). In some embodiments, a different value may be used to indicate the type of cell (e.g., LTE, NSA, 5G, and the like). The acquisition database155is used during UE startup or out of service search to quickly prioritize selection of a suitable NSA cell if one is known within the acquisition database155and meets the selection criteria for the UE. Flowchart400describes the startup prioritization procedure in more detail. Acquisition database155is further used during the 5G preferred NSA background search575that is described with respect toFIG. 5in further detail. In the 5G preferred NSA background search575, used when the UE is camped on an LTE only cell, the acquisition database155is used to identify NSA cell frequencies to scan for NSA cells to move to before performing a band scan of all bands. By scanning known NSA frequency bands first, the UE may find a suitable NSA cell first to camp on. After finding an NSA cell to camp on, the UE stops searching and configures settings to help ensure the UE does not move off the NSA cell as discussed with respect to flowchart600ofFIG. 6.

FIG. 3illustrates an example fingerprint database305. Fingerprint database305includes entries for LTE only cells and corresponding neighboring NSA cells. As shown inFIG. 3with example data, LTE only cell having cell identifier C1and frequency F1has two neighbor NSA cells. NSA cell having cell identifier C3and frequency F1is neighboring LTE only cell having cell identifier C1, and NSA cell having cell identifier C4and frequency F2is neighboring LTE only cell having cell identifier C1. The UE can add entries into fingerprint database160upon camping on an NSA cell or an LTE only cell to identify the neighboring cells for entry into fingerprint database160. Fingerprint database160is then used as the initial step to identify any known neighboring NSA cells when the UE is camped on an LTE only cell. For example, if the UE is camped on LTE only cell having identifier C2and frequency F3, using fingerprint database160, the UE can identify that NSA cell having cell identifier C5and frequency F4is neighboring. Accordingly, the UE can scan frequency F4for NSA cell C5to determine if C5is a suitable serving cell for the UE. If so, the UE can reselect and move to C5from C2. If C5is not available or suitable for the UE to camp on, the UE can execute the 5G preferred NSA background search575as described in further detail with respect toFIG. 5.

FIG. 4illustrates an example flowchart400for preferred selection of an NSA serving cell (e.g., NSA cell115) on startup of a UE (e.g., UE105). When the UE initializes on startup or when the UE is removed from a serving cell for any reason, the UE may execute flowchart400by startup subsystem145. At decision block405the UE determines whether an NSA cell is in the acquisition database (e.g., acquisition database155). The UE can check the NSA cell flag210in the acquisition database155entries to identify an NSA cell to attempt to connect to so that the NSA cell is the serving cell for the UE. In some embodiments, the UE starts with the first entry to determine whether the NSA cell flag is set to true. In the example acquisition database155shown inFIG. 2, the first entry for cell identifier0has the NSA cell flag210set to TRUE. Accordingly, the UE can scan frequency1215for Cell0. If Cell0meets the selection criteria, the UE can connect to Cell0to be the serving cell for the UE. If Cell0does not meet the selection criteria for the UE, the UE can check the second entry. In the example acquisition database155inFIG. 2, the second entry has an NSA cell flag210value of FALSE, so the UE checks the third entry. This process continues until the UE either identifies an NSA cell that meets the selection criteria for the UE or the UE has not found an entry after checking all of the entries that have the NSA cell flag210set to TRUE and the corresponding NSA cell meets the selection criteria for the UE.

At decision block410, the UE determines whether an NSA cell was found in the acquisition database155that is suitable for camping. If so, the UE camps on the NSA cell at step445. If not, the UE checks the acquisition database at decision block415for an LTE only cell. In the example acquisition database155ofFIG. 2, the UE may start at the beginning of the acquisition table155and determine that the first entry has the NSA cell flag210value set to TRUE, so the UE then checks the second entry, which in the example has the NSA cell flag210value set to FALSE. The UE scans frequency2256for cell identifier3to see if Cell3meets the selection criteria of the UE. If not, the UE checks the next entry in the acquisition database155. This process continues until the UE either identifies an LTE only cell that meets the selection criteria for the UE or the UE has not found an entry after checking all of the entries that have the NSA cell flag210set to FALSE and the corresponding LTE only cell meets the selection criteria for the UE.

At decision block420, the UE determines whether an LTE only cell was found in the acquisition database155that is suitable for camping. If so, the UE camps on the LTE only cell at step440. If not, the UE executes a band scan. In some embodiments, the UE will not scan frequency bands already scanned from the acquisition database155to avoid duplicate unnecessary processing and battery consumption. At decision block430, the UE determines if the band scan has identified a frequency having a cell that is meets the selection criteria for the UE. In some embodiments, during the band scan, the goal is for the UE to get service, regardless of which type of cell, as quickly as possible because until the UE is connected to a serving cell, the UE is not connected to any mobile communication network. If the band scan completes without finding a suitable cell for a serving cell that meets the selection criteria of the UE, the UE continues to execute the band scan until a suitable cell for camping on is identified. At decision block435, the UE determines if the cell that is suitable for camping on is an NSA cell or an LTE only cell. If the cell is an NSA cell, the UE camps on the NSA cell at step445. The UE may then, in some embodiments, continue to execute flowchart600. If the cell is an LTE only cell, the UE camps on the LTE only cell at step440. The UE may then, in some embodiments, execute flowchart500.

Upon completion of flowchart400, the UE is camped on either an NSA cell or an LTE cell. While NSA cells are initially prioritized, because the UE is not connected to any cell during performance of flowchart400, the UE does not forego connecting to an LTE only cell that is suitable to continue searching for an NSA cell. Rather, the UE will connect to the LTE only cell and then proceed to expedite preferred reselection of an NSA cell as discussed with respect to flowchart500ofFIG. 5.

FIG. 5illustrates an example flowchart500for preferred reselection of an NSA serving cell (e.g., NSA cell115) for a UE (e.g., UE105) when an LTE only cell (e.g., LTE only cell110) is the serving cell for the UE. At decision block505, the UE determines whether the LTE only cell is in the fingerprint database160. If the LTE cell is in the fingerprint database160, the UE evaluates any associated neighboring NSA cells listed in the fingerprint database160. For example, if the UE is camping on Cell C1at frequency F1, the UE evaluates Cell C3on frequency F1and Cell C4on frequency F2. This evaluation process is described with respect to flowchart700ofFIG. 7.

FIG. 7illustrates an example flowchart700for a UE (e.g., UE105) to more quickly reselect an NSA cell (e.g., NSA cell115) if the serving cell for the UE is an LTE only cell (e.g., LTE only cell110). At step705, the UE temporally increases all NSA cell reselection priority to the highest values, which is higher than the serving frequency priority for the serving cell. Using the example of fingerprint database160and that the UE is camping on Cell C1on frequency F1, the UE temporally increases the NSA cell reselection priorities for Cell C3on frequency F1and for Cell C4on frequency F2to a higher priority than the priority set for Cell C1at frequency F1.

At step710, the UE ranks the NSA cells based on signal quality or signal strength. Continuing with the example above, Cell C3and Cell C4are ranked. For the purposes of this example, Cell C3is ranked higher than Cell C4.

At step715, the UE selects the highest ranking NSA cell. In this example, the UE selects Cell C3. At step720, Cell C3at frequency F1is evaluated using reselection criteria. In some embodiments, the reselection criteria is the legacy reselection criteria used in systems that do not have the 5G NSA preferred mode. If Cell C3does not meet the reselection criteria, Cell C4is evaluated.

Returning toFIG. 5, at decision block515, the UE determines whether the evaluation at step510resulted in finding a suitable NSA cell. If a suitable cell is found at decision block515, the UE camps on the NSA cell at step525. If the evaluation did not result in a suitable NSA cell, the UE executes timer1at step520. The UE executes timer1at step520if, at decision block505the LTE only cell the UE is camping on is not in the fingerprint database160.

Executing timer1at step520is the first in a series of steps that are the preferred NSA background search575shown by the dashed box. Timer1may be, for example a 5-second timer that simply creates a delay before further searching is completed by the UE to avoid constant searching resulting in battery drain of the UE. The UE checks at decision block535for a suitable NSA cell listed in the acquisition database155. In some embodiments, the UE starts with the first entry looking for whether the entry has the NSA cell flag value set to TRUE. If so, the UE scans the NSA cell frequency associated with the first entry for the cell identifier to measure whether the NSA cell meets the selection criteria. If not, the UE moves to the next entry in the acquisition database155until the UE either runs out of entries in the acquisition database or finds an NSA cell that meets the selection criteria. If the UE finds an NSA cell that meets the selection criteria, the UE updates the fingerprint database160. In this example, the UE is camping on LTE only cell C1, and neither of Cells C3or C4were suitable from the fingerprint database160. However, the UE can update the fingerprint database160with the discovered neighbor NSA cell found as another NSA cell associated with LTE only cell C1. At step525the UE can camp on the NSA cell.

If the UE did not find a suitable NSA cell in the acquisition database at decision block535, the UE can determine if there is a suitable NSA cell in the neighbor cell frequency list at decision block540. The neighbor cell frequency list is provided by the LTE only cell (e.g., C1) that the UE is camped on, which is configured by the network (e.g., in system information block5). The UE can scan the frequencies in the neighbor cell frequency list to determine if one of the NSA cells associated with one of the neighbor cell frequencies in the list meets the selection criteria (i.e., reselection criteria) for the UE. If the UE finds a suitable NSA cell in the neighbor cell frequency list, the UE can update the fingerprint database160with the new NSA cell information (e.g., associated with LTE only cell C1in the example) at step530. At step525, the UE can camp on the NSA cell.

If the UE did not find a suitable NSA cell in the neighbor cell frequency list, the UE can determine whether there is a suitable NSA cell in the remaining frequency bands at decision block545. In particular, the UE may first scan frequency bands derived from the acquisition database155NSA cells. This scan provides another opportunity of utilizing the acquisition database in relation to the remaining frequency bands before proceeding to the subsequent process. If no suitable NSA cells are found, then the priority band list is scanned for a suitable NSA cell. The priority band list is stored in memory of the modem135. If no suitable NSA cells are found, then the remaining frequency bands are scanned for an NSA cell. If a suitable NSA cell is found as derived from the acquisition database155, the priority band list, or the remaining frequency bands, the UE updates the fingerprint database160at step530and camps on the NSA cell at step525. If no suitable NSA cell is identified at decision block545, the UE increments the counter at step550. The counter is used to ensure that the preferred NSA background search575does not continue searching despite no available NSA cells as that would drain the battery of the UE. Accordingly, at decision block555, the UE determines if the counter is greater than or equal to a threshold. The threshold may be, for example, 5, so that the UE executes the preferred NSA background search575five times before the counter reaches the threshold. If the counter is equal to or greater than the threshold, the UE disables the 5G preferred NSA mode at step565. Disabling the 5G preferred NSA mode may include, for example, resetting the timers (timer1and timer2), resetting the counter, and stopping the preferred NSA background search575. In some embodiments, disabling the feature may include setting a flag to false to indicate the preferred mode methods should not be performed. Note that the 5G preferred NSA mode may be reenabled when the user location changes such that the user may have to switch cells from the LTE only cell currently camped on, indicating new NSA cells may be available in the new location for selection.

At decision block555if the UE determines the counter is less than the threshold, the UE executes the timer2, which is typically a slightly longer timer than timer1. For example, if timer1is 5 seconds, timer2may be 30 seconds. The timer delay helps ensure that sufficient time passes before the preferred NSA background search575executes again to avoid excessive power consumption.

FIG. 6illustrates an example flowchart600for a UE (e.g., UE105) when an NSA cell (e.g., NSA cell115) is the serving cell for the UE (i.e., the UE is camped on the NSA cell). When the UE is camped on an NSA cell, the UE may reselect to an LTE only cell because the LTE only cell has a higher priority or better signal. To avoid this unwanted reselection, flowchart600may be performed by the UE to encourage the UE to remain on the NSA cell. Flowchart600begins with the UE stopping the timers and resetting the timers and counter at step605. The UE may stop the preferred NSA background search575at step610to avoid searching for additional NSA cells. This will maintain batter power for the UE. At step615, the UE may update the acquisition database155with the NSA cell information of the serving cell for the UE. At step620, the UE may update the fingerprint database160with discovered NSA cell information and any associated known LTE only cell information. At step625, the UE may temporally increase the first threshold for high priority LTE only neighboring cell and temporally increase an offset for intra frequency/equal priority inter frequency LTE only neighbor cells if the serving NSA cell is above a threshold value. Ensuring the serving NSA cell is above a threshold value helps ensure the UE does not stay camping on an inferior cell. Increasing the first threshold for the high priority LTE only neighbor cell and the offset for the intra frequency/equal priority inter frequency LTE only neighbor cells ensures that it is more difficult for the UE to reconnect to the LTE only neighbor cell. Accordingly, the UE is more likely to remain camped on the NSA cell.

FIG. 8illustrates a method800for a UE (e.g., UE105) to preferably select an NSA cell (e.g., NSA cell115) as the serving cell during startup of the UE. The method800may be performed by the application processor of the UE based on instructions stored in the memory of the UE. In some embodiments, some portions of the method800may be performed by, for example, the modem of the UE.

Method800begins at step805with the UE (e.g., UE105) searching an acquisition database (e.g., acquisition database155) for an entry marked with a first value for an NSA flag (e.g., NSA flag210) indicating the associated entry is for an NSA cell. For example, the UE identifies a first entry in the acquisition database to determine if the first entry is associated with an NSA cell, if not, the UE checks the second entry in the acquisition database and so forth until the UE finds an NSA cell in the acquisition database or runs out of entries.

At step810, if the UE determines that the NSA cell meets the cell selection criteria, the UE camps on the NSA cell associated with the entry marked as an NSA cell. If, the UE determines that the NSA cell does not meet the cell selection criteria, or if the UE does not find an entry marked as an NSA cell in the acquisition database, the UE searches the acquisition database for entries marked with the NSA flag indicating the associated cell is an LTE only cell at step815. The UE may check the first entry and, if the entry does not indicate the entry is for an LTE only cell, the UE may check the next entry and so forth until the UE finds an LTE only cell in the acquisition database or runs out of entries.

At step820, if the UE determines that the LTE only cell identified in the acquisition database meets the cell selection criteria, the UE camps on the LTE only cell associated with the entry marked as an LTE only cell. If the UE determines that the LTE only cell does not meet the cell selection criteria, or if the UE does not find an entry marked as an LTE only cell in the acquisition database, the UE executes a band scan at step825. The band scan may be a scan of all frequencies to find any suitable cell for the UE to camp on to provide service to the UE.

FIG. 9illustrates a method900for a UE (e.g., UE105) to preferably reselect an NSA cell (e.g., NSA cell115) as the serving cell when the UE is camped on an LTE only cell (e.g., LTE only cell110). If, in method800the UE camped on an LTE only cell, method900may be executed to attempt to find an NSA cell to serve the UE. Method900begins with the UE searching the fingerprint database (e.g., fingerprint database160) for a discovered neighbor NSA cell associated with the LTE only cell at step905. If the UE finds a discovered neighbor NSA cell in the fingerprint database, the UE measures the frequency associated with the discovered neighbor NSA cell for reselection at step910. If the UE determines that the discovered neighbor NSA cell is not suitable or if there is no discovered neighbor NSA cell in the fingerprint database, the UE executes the NSA background search (e.g., preferred NSA background search575) to attempt to find an NSA cell to select in place of the LTE only cell the UE is camped on.

FIG. 10illustrates examples of components of a computer system1000according to certain embodiments. The computer system1000may be, for example, user equipment105as described with respect toFIG. 1. Although these components are illustrated as belonging to a same computer system1000, the computer system1000can also be distributed.

The computer system1000includes at least a processor1002(e.g., application processor130), a memory1004(e.g., memory140), a storage device1006, input/output peripherals (I/O)1008, communication peripherals1010, and an interface bus1012. The interface bus1012is configured to communicate, transmit, and transfer data, controls, and commands among the various components of the computer system1000. The memory1004and the storage device1006include computer-readable storage media, such as RAM, ROM, electrically erasable programmable read-only memory (EEPROM), hard drives, CD-ROMs, optical storage devices, magnetic storage devices, electronic non-volatile computer storage, for example Flash® memory, and other tangible storage media. Any of such computer readable storage media can be configured to store instructions or program codes embodying aspects of the disclosure. The memory1004and the storage device1006also include computer readable signal media. A computer readable signal medium includes a propagated data signal with computer readable program code embodied therein. Such a propagated signal takes any of a variety of forms including, but not limited to, electromagnetic, optical, or any combination thereof. A computer readable signal medium includes any computer readable medium that is not a computer readable storage medium and that can communicate, propagate, or transport a program for use in connection with the computer system1000.

Further, the memory1004includes an operating system, programs, and applications. The processor1002is configured to execute the stored instructions and includes, for example, a logical processing unit, a microprocessor, a digital signal processor, an application processor, and other processors. The memory1004and/or the processor1002can be virtualized and can be hosted within another computer system of, for example, a cloud network or a data center. The I/O peripherals1008include user interfaces, such as a keyboard, screen (e.g., a touch screen), microphone, speaker, other input/output devices, and computing components, such as graphical processing units, serial ports, parallel ports, universal serial buses, and other input/output peripherals. The I/O peripherals1008are connected to the processor1002through any of the ports coupled to the interface bus1012. The communication peripherals1010(e.g., modem135) are configured to facilitate communication between the computer system1000and other computing devices over a communications network and include, for example, a network interface controller, modem, wireless and wired interface cards, antenna, and other communication peripherals.