OPTIMIZED RADIO LINK FAILURE RECOVERY FOR CELLS REPORTED IN MEASUREMENT REPORT

Techniques for recovering quickly from a radio link failure (RLF) by identifying potentially strong candidate cells, while avoiding the conventional delays from relying only on initial ACQ DB scans followed by band-scanning, are disclosed. In one aspect, a wireless apparatus such as a user equipment (UE) may identify a radio link failure (RLF) of an existing wireless connection. The UE may prioritize, during an RLF recovery procedure for restoring the connection, candidate cells using connection criteria from one or more measurement reports. The UE can thereupon restore the connection using a cell having a highest priority. In various configurations, the UE can use cells from A3, A4, A5, inter-RAT or periodic measurement reports to reestablish a stronger connection in a faster time.

TECHNICAL FIELD

The present disclosure generally relates to communication systems, and more particularly, to recovering from radio link failures in wireless connections.

DESCRIPTION OF THE RELATED TECHNOLOGY

SUMMARY

A user equipment (UE) may experience a radio link failure (RLF) during a wireless connection for a number of reasons. Often, RLF occurs as a result of a gradual or sudden drop in signal quality. Signal quality deterioration is typically precipitated by device interference arising from factors like moving obstacles, changing terrain, increasing distances from base stations, other signals in or near the same frequency band, and the like. Upon occurrence of an RLF in connected mode, it is desirable to recover and reestablish the link as quickly and seamlessly as possible. Conventionally, a UE may perform cell selection in a radio resource control (RRC) connection reestablishment procedure. As part of cell selection in this RRC mode, the UE scans the frequencies of last camped cells and other cells in the UE's acquisition database (ACQ DB). In the case where none of the cells in the ACQ DB are suitable to reestablish the connection (e.g., the respective signal qualities are insufficient), the UE may next trigger a band scan to effect a more comprehensive scan of different frequencies. These band scans may be time consuming and may delay RLF recovery. In another case where the UE finds a suitably strong cell during recovery but the cell is recognizably not a preferred cell of the UE, the UE may spend additional time scanning frequencies to find a preferred cell before reestablishing a link. Recovering from RLF can consequently result in long delays, and in some cases the selection of cells that considerably reduce throughput.

Accordingly, in one configuration, as an alternative to simply scanning the last camped cells in the ACQ DB, followed where needed by band-scanning, the UE may prioritize candidate cells reported in the measurement reports including, for example, the A3/A4/A5, inter-radio access technology (RAT) or periodic measurement reports using connection criteria such as one or more reported measurements of signal strength, signal quality, signal-to-noise ratio, or the like. The connection criteria may include as-reported values of these parameters, or weighted or averaged values of these parameters instead. These connection criteria may include, for example, reference signal received power (RSRP), reference signal received quality (RSRQ), a received signal strength indicator (RSSI), or another measurement quantity. The connection is thereupon restored using the connection criteria to identify a candidate cell having the highest priority. A cell with the highest priority may correspond, for example, to the candidate cell with the highest signal strength. In one configuration, prioritization is restricted to cells that satisfy a minimum measurement quantity threshold value to ensure that weak cells are not prioritized. If the measurement reports do not yield favorable candidate cells, the UE can continue cell selection based on the conventional ACQ DB.

In another configuration, when RLF occurs the UE can perform cell selection beginning with prioritizing strong cells based on the measurement reports as described above. In this configuration, however, the UE may give initial or special priority to cells from the measurement reports that belong to a preferred cell database corresponding to a feature supported by the UE. Examples of such preferred criteria may include HST (high speed transport) or, in the case of LTE, E-TRAN dual connectivity (ENDC), among others.

In an aspect of the disclosure, a method, a computer-readable medium, and an apparatus are provided. The apparatus includes one or more memories, and one or more processors each communicatively coupled with at least one of the one or more memories. The one or more processors, individually or in any combination, are operable to cause the apparatus to identify a radio link failure (RLF) of an existing wireless connection, prioritize, during an RLF recovery procedure for restoring the connection, candidate cells using connection criteria from one or more measurement reports, and restore the connection using the candidate cell having a highest priority.

DETAILED DESCRIPTION

In some aspects, the base stations102may communicate directly or indirectly (e.g., through the EPC160or core network190) with each other over third backhaul links134(e.g., X2 interface). The first backhaul links132, the second backhaul links184, and the third backhaul links134may be wired or wireless. At least some of the base stations102may be configured for integrated access and backhaul (IAB). Accordingly, such base stations may wirelessly communicate with other such base stations. For example, at least some of the base stations102configured for IAB may have a split architecture that includes at least one of a central unit (CU), a distributed unit (DU), a radio unit (RU), a remote radio head (RRH), and/or a remote unit, some or all of which may be collocated or distributed and/or may communicate with one another. In some configurations of such a split architecture, the CU may implement some or all functionality of a radio resource control (RRC) layer, whereas the DU may implement some or all of the functionality of a radio link control (RLC) layer.

Illustratively, some of the base stations102configured for IAB may communicate through a respective CU with a DU of an IAB donor node or other parent IAB node (e.g., a base station), further, may communicate through a respective DU with child IAB nodes (e.g., other base stations) and/or one or more of the UEs104. One or more of the base stations102configured for IAB may be an IAB donor connected through a CU with at least one of the EPC160and/or the core network190. In so doing, the base station(s)102operating as an IAB donor(s) may provide a link to the one of the EPC160and/or the core network190for other IAB nodes, which may be directly or indirectly (e.g., separated from an IAB donor by more than one hop) and/or one or more of the UEs104, both of which may have communicate with a DU(s) of the IAB donor(s). In some additional aspects, one or more of the base stations102may be configured with connectivity in an open RAN (ORAN) and/or a virtualized RAN (VRAN), which may be enabled through at least one respective CU, DU, RU, RRH, and/or remote unit.

The electromagnetic spectrum is often subdivided, based on frequency/wavelength, into various classes, bands, channels, etc. In 5G NR, two initial operating bands have been identified as frequency range designations FR1 (410 MHz-7.125 GHz) and FR2 (24.25 GHz-52.6 GHz). The frequencies between FR1 and FR2 are often referred to as mid-band frequencies. Although a portion of FR1 is greater than 6 GHz, FR1 is often referred to (interchangeably) as a “sub-6 GHz” band in various documents and articles. A similar nomenclature issue sometimes occurs with regard to FR2, which is often referred to (interchangeably) as a “millimeter wave” (or “mmWave” or simply “mmW”) band in documents and articles, despite being different from the extremely high frequency (EHF) band (30 GHz-300 GHz) which is identified by the International Telecommunications Union (ITU) as a “millimeter wave” band.

Referring again toFIG.1, in certain aspects, the UE104may be configured to include cell prioritizing component198. As discussed herein in various configurations, cell prioritizing component198may be configured, upon identifying an RLF, to consider different connection criteria included in (or derived from) measurement reports that have been provided to the UE to date, in lieu of simply reviewing the prior camped-on cells in the ACQ DB. Cell prioritizing component198may in some configurations review connection criteria relating to signal strength included in A3, A4, or A5measurement reports, for example, or in inter-RAT or periodic measurement reports and other measurement reports that may have been received at the UE prior to RLF and that may include signal quality or link-based information. Cell prioritizing component198may review this criteria, such as reference signal received power (RSRP), reference signal received quality (RSRQ), received signal strength indicator (RSSI), signal-to-noise ratios, and other parameters that may be provided. Connection criteria reviewed by the cell prioritizing component198may not just include the values from the reports without more; in other configurations, prioritizing component198may consider average values over time, absolute values, average powers or other values corresponding to cells over a plurality of most recently received measurement reports, and other similar connection criteria that would enable the prioritizing component198to prioritize, or rank, the quality or desirability of cells in the event RLF occurs so that the connection can be reestablished (e.g., via an RRC Connection Reestablishment procedure) as quickly and efficiently as possible.

In other configurations described further herein, the connection criteria may also relate to preferred cell features, such as any one or more of high-speed transport (HST), Evolved Universal Terrestrial Radio Access Network Dual Connectivity (ENDC), evolved multimedia broadcast/multicast service (eMBMS), or closed subscriber group (CSG). It may be the case that prior to RLF, the cell was communicating via one of these features, or another preferred feature provided in a governing standard or from a wireless carrier. Cell prioritizing component198may identify one or more candidate cells that belong to a preferred cell database corresponding to one or more of these features, in which case the link or connection can be reestablished using the preferred feature. In some configurations, the cell prioritizing component198involves first prioritizing cells that include preferred features corresponding to the UE that lost the connection, and thereafter prioritizing cells based on signal quality as described above. In other configurations, either or both of these prioritization techniques may, to ensure that weak links are not selected, only prioritize those cells that have some minimum threshold signal power, such as some RSRPthreshvalue, for example. In this way, cell prioritization component198will only prioritize cells that can viably be used in a connection, whether based primarily on signal power, preferred features, or otherwise.

Although the present disclosure may focus on 5G NR, the concepts and various aspects described herein may be applicable to other similar areas, such as LTE, LTE-Advanced (LTE-A), Code Division Multiple Access (CDMA), Global System for Mobile communications (GSM), or other wireless/radio access technologies. In these cases, different radio access technologies may correspond to different preferred features, and cell prioritization component198may prioritize cells with distinct preferred features not only depending on the requirements of the UE, but also on the specific RAT in employment.

FIG.2Ais a diagram200illustrating an example of a first subframe within a 5G NR frame structure.FIG.2Bis a diagram230illustrating an example of downlink channels within a 5G NR subframe.FIG.2Cis a diagram250illustrating an example of a second subframe within a 5G NR frame structure.FIG.2Dis a diagram280illustrating an example of uplink channels within a 5G NR subframe. The 5G NR frame structure may be frequency division duplexed (FDD) in which for a particular set of subcarriers (carrier system bandwidth), subframes within the set of subcarriers are dedicated for either downlink or uplink, or may be time division duplexed (TDD) in which for a particular set of subcarriers (carrier system bandwidth), subframes within the set of subcarriers are dedicated for both downlink and uplink. In the examples provided byFIGS.2A,2C, the 5G NR frame structure is assumed to be TDD, with subframe4being configured with slot format28(with mostly downlink), where D is downlink, U is uplink, and F is flexible for use between downlink/uplink, and subframe3being configured with slot format34(with mostly uplink). While subframes3,4are shown with slot formats34,28, respectively, any particular subframe may be configured with any of the various available slot formats0-61. Slot formats0,1are all downlink, uplink, respectively. Other slot formats2-61include a mix of downlink, uplink, and flexible symbols. UEs are configured with the slot format (dynamically through downlink control information (DCI), or semi-statically/statically through RRC signaling) through a received slot format indicator (SFI). Note that the description infra applies also to a 5G NR frame structure that is TDD.

As illustrated inFIG.2A, some of the REs carry at least one pilot and/or reference signal (RS) for the UE. In some configurations, an RS may include at least one demodulation RS (DM-RS) (indicated as Rxfor one particular configuration, where100xis the port number, but other DM-RS configurations are possible) and/or at least one channel state information (CSI) RS (CSI-RS) for channel estimation at the UE. In some other configurations, an RS may additionally or alternatively include at least one beam measurement (or management) RS (BRS), at least one beam refinement RS (BRRS), and/or at least one phase tracking RS (PT-RS).

At the UE350, each receiver354RX receives a signal through its respective antenna352. Each receiver354RX recovers information modulated onto an RF carrier and provides the information to the one or more receive (RX) processors356. The one or more TX processors368and the one or more RX processors356implement layer 1 functionality associated with various signal processing functions. The one or more RX processors356may perform spatial processing on the information to recover any spatial streams destined for the UE350. If multiple spatial streams are destined for the UE350, they may be combined by the one or more RX processors356into a single OFDM symbol stream. The one or more RX processors356then converts the OFDM symbol stream from the time-domain to the frequency domain using a Fast Fourier Transform (FFT). The frequency domain signal comprises a separate OFDM symbol stream for each subcarrier of the OFDM signal. The symbols on each subcarrier, and the reference signal, are recovered and demodulated by determining the most likely signal constellation points transmitted by the base station310. These soft decisions may be based on channel estimates computed by the channel estimator358. The soft decisions are then decoded and deinterleaved to recover the data and control signals that were originally transmitted by the base station310on the physical channel. The data and control signals are then provided to the one or more controllers/processors359, which implement layer 3 and layer 2 functionality.

The one or more controllers/processors359may each be associated with one or more memories360that store program codes and data. The one or more memories360, individually or in any combination, may be referred to as a computer-readable medium. In the UL, the one or more controllers/processors359provide demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, and control signal processing to recover IP packets from the EPC160. The one or more controllers/processors359are also responsible for error detection using an ACK and/or NACK protocol to support HARQ operations.

Channel estimates derived by a channel estimator358from a reference signal or feedback transmitted by the base station310may be used by the one or more TX processors368to select the appropriate coding and modulation schemes, and to facilitate spatial processing. The spatial streams generated by the one or more TX processors368may be provided to different antenna352via separate transmitters354TX. Each transmitter354TX may modulate an RF carrier with a respective spatial stream for transmission.

The one or more controllers/processors375may each be associated with one or more memories376that store program codes and data. The one or more memories376, individually or in any combination, may be referred to as a computer-readable medium. In the UL, the one or more controllers/processors375provide demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, control signal processing to recover IP packets from the UE350. IP packets from the one or more controllers/processors375may be provided to the EPC160. The one or more controllers/processors375are also responsible for error detection using an ACK and/or NACK protocol to support HARQ operations.

At least one of the one or more TX processors368, the one or more RX processors356, and the one or more controllers/processors359may be configured to perform aspects in connection with cell prioritizing component198ofFIG.1.

In conventional wireless networks, when RLF occurs in connected mode, the UE performs cell selection to recover from the RLF. More specifically, as part of cell selection for RLF recovery, the UE may scan the last camped cells and other cells included in the UE's acquisition database (ACQ DB). When none of the cells listed in the ACQ DB are suitable for cell selection, such as there are no adjacent cells or the cells' signal properties such as RSRP are too weak to sustain a connection, the UE may have to perform a more comprehensive frequency band scan to identify a suitable cell or channel to reestablish the connection. This band scan may be time consuming, meaning that the recovery from the RLF can be delayed, sometimes significantly, before an adequate connection can be reestablished. In other cases, the UE may find a suitable cell during RLF recovery that is not a preferred cell. That is to say, in some arrangements a UE may be designated via a preferred cell database or other notification to establish wireless connections by means of a preferred cell feature from a governing standard, for example, or as dictated from a wireless carrier. In these cases, where the UE is limited to the conventional cell selection techniques described herein, a potentially significant delay may occur before the UE can return to the preferred cell. These conventional techniques may reduce overall throughput, both for ordinary connections and those connections involving preferred or special features of the cell.

FIG.4is a flowchart400of a conventional method of wireless communication performed by a UE. It is assumed that at402, an RLF occurs and the UE identifies a RLF trigger, such as an interrupted connection or dropped call. At404, the UE may commence a cell selection procedure for RLF recovery404. At406, the UE may scan frequencies from an ACQ DB to find a suitable cell for camping. The ACQ DB may include, for example, an historic list of cell previously camped on by the UE. The UE then considers whether a suitable cell has been found from the ACQ DB for which the connection can be reestablished. If a suitable cell has been found that meets the necessary power and signal strength criteria, the UE may trigger a radio resource control (RRC) Reestablishment request at410. Otherwise, at412, the UE may trigger a band scan to identify frequencies to perform cell selection. If no candidate frequencies are found, the UE will continue the band scanning. The band scanning may continue until a useable cell is identified. If at416the band scan reveals candidate frequencies for possible use in a cell selection, the UE at416may thereupon scan the frequencies from the band scan results to find a suitable cell. Once such a cell is found (408), the UE can trigger an RRC connection reestablishment request.

One item of note is, that even if the ACQ DB or the band scan successfully results in a cell selection that yields a reconnection, the process may impose a substantial time delay. Another item is that, if the UE was using a preferred feature (e.g., HST, or an anchor cell supporting LTE-NR ENDC, etc.), finding another suitable cell with the preferred feature may be an arbitrary undertaking. That is to say, the conventional scan focuses on cells with specific link quality criteria, without taking into account cells having preferred features. Reconnection performance can in many cases be sub-optimal as a consequence. One possibility is that none of the cells in the ACQ DB of the UE are strong enough in the location of the RLF, which requires the UE to trigger the time-consuming band scan to find a suitable cell. Another possibility, as noted, is that a UE preferring a feature such as HST (among others) may not be able to recover from the RLF on an HST, cell, which also degrades performance.

FIG.5is a timing diagram showing a basic RLF recovery using certain aspects of the disclosure. The UE504can, for instance, be the UE104with cell prioritizing component198inFIG.1. In the illustration shown, only one UE504is shown, and it is assumed that the UE504has established a connection with another unseen device (e.g., another UE) via base station502. At506, an RLF event is triggered at the UE504. At510, UE504may commence cell selection using a prioritization cycle. In the example shown, the UE504can use one or more of measurement reports A3, A4, and A5, B1and B2to elicit different values from the measurement reports including RSRP, RSRQ, and others. The elicited values or connection criteria may be absolute, or the connection criteria may be instead computed based on the obtained values—a weighted average over some amount of time or some number of received reports at the UE, for example. The measurement reports may reveal cells with highly desirable properties and on which the UE504can initiate connection reestablishment, if desired, without the delays and disadvantages associated with relying solely on the ACQ DB and disregarding the measurement reports. In still other configurations, the UE may extend its prioritization to inter-RAT measurement reports, periodic measurement reports and other information in the UE's possession at the time of the RLF. Using this information from the measurement reports and other measurement quantity thresholds for prioritization and comparison purposes, the UE may proceed to prioritize cell selection, e.g., with the highest priority candidate cells being the strongest in power or signal-to-noise ratio and the lowest being the weakest.

In other configurations, at512, the UE may also prioritize cells not only on the basis of the strength of the cell or its desirable weighted or absolute connection criteria, but on the presence or absence of preferred features that correspond to a preferred feature in the UE's database. Examples include, without limitation, HST, eMBMS, CSG, ENDC, and any other preferred features provided by the applicable standards-governing body or the wireless carrier in use. Thus, for example, the UE may initially prioritize those cells that have preferred cell features, with the candidate cells ideally having the strongest and most desirable RSRP/RSRQ/etc. values along with the most desirable preferred features as the highest priority cells, with less strong preferred cells and/or strong non-preferred cells as the next group in the priority line, and with non-preferred cells and weak cells at the lowest priority. At514, having identified a candidate cell with the highest priority (which may include a combination of high signal strength and a preferred feature) the UE504can send the base station502a request for connection reestablishment. Conversely, if the measurement reports do not yield any candidate cells, or suitable candidate cells, the UE can still perform the steps inFIG.4of scanning bands on the ACQ DB database (516), followed by the band scan. Thus, aspects of the disclosure can optionally be coupled with the conventional methods, the latter being used solely as an alternative to increase overall likelihood of connection. Unlike conventional techniques, however, this latter alternative can be interrupted if new connection criteria are found concerning a potentially viable candidate cell.

Moreover, the UE504has a higher probability of reestablishing the connection after RLF using a preferred cell or a strong cell identified from the readily available measurement reports, and doing so at a faster rate with less delay than conventional techniques.

In some configurations, regardless of whether prioritization takes into account only the link-quality connection criteria in the measurement reports, or whether the connection criteria also includes information identifying the preferred features in the preferred cell database, the UE may require in both arrangements that each of the candidate cells satisfies an initial reference signal threshold (e.g., RSRPthresh) to ensure that prioritization does not include weak cells likely to cause additional RLFs. If no such cell has connection criteria exceeding this threshold value in the current measurement reports (e.g., A3, A4, A5), the UE can proceed to resort to the ACQ DB for cell selection, as noted above.

In some configurations, cell prioritization is updated after every measurement report is received at the UE, so that the prioritization information in the UE is as accurate and as up-to-date as possible. In additional configurations, the more recently reported cells can replace older or antiquated cells for the same reporting event type, to further ensure that prioritization of candidate cells remains updated. These techniques can also help assure that preferred features in the vicinity of the RLF are continually updated and tracked for use in cell prioritization. In additional implementations as noted above, the UE may keep track of cells that are reported in the B1and B2measurement reports, so that the UE can notify the target radio access technology (RAT) accordingly. The RAT can beneficially make use of these cells when cell selection occurs involving the target RAT. In yet additional implementations, the measurement report-based cell prioritization aspects disclosed herein may be maintained throughout a period, such as throughout the RRC connection until UE goes idle, or until another specified time.

As noted above, in addition to cell prioritization based on cell strength, the LIE can perform RLF recovery on preferred cells. However, the relative importance given different connection criteria may differ, and may be tuned to the needs of a particular carrier. In some configurations, the order of prioritization may occur as follows. First, strong candidate cells reported in A3, A4or A5measurement reports may be given the biggest consideration in prioritization. Thereafter, candidate cells that belong to a preferred cell database, depending on the feature preferred by the UE, can be prioritized. In these configurations, it may follow that cells that are both the strongest and that have the most desirable preferred features in the UE database of preferred cells may be initially prioritized at the top of the list. In other embodiments, the two considerations may be partitioned into two sets of prioritizations, with some logical algorithm taking into account the relative importance of the preferred feature at issue versus the relative signal strength corresponding to the cell.

In general, during RLF recovery, the UE should prioritize cell selection to the preferred cell based on the identified ranking as long as the cell also satisfies some threshold RSRP requirement to ensure that weak cells are not prioritized. As part of this solution, the UE may maintain different preferred cell databases that each take into account the cell ID and its specific feature(s), if any (e.g., HST, ENDC, CSG, and the like). In still other configurations, among the strong candidate cells that got reported in the measurement reports, the UE may prioritize these strong cells based on the presence or absence of these strong cells in different feature databases. In other configurations, the UE may consider a single, consolidated database that maintains each of the cells and their supported features.

FIG.6is a depiction600of database or table entries used during cell selection. In one configuration involving cell selection, the data from the measurement reports may be included with entries602. The following is an exemplary prioritization procedure that may be conducted. In a first configuration, the data in table entries602represent prioritized entries from one or more of the measurement reports (MR). The UE is considered to have the following Connected Measurement configuration from the network:1. MeasId x for MeasObj ID x and reportConfig ID x for MR A32. MeasId y for MeasObj ID y and reportConfig ID y for MR A43. MeasId z for MeasObj ID z and reportConfig ID z for MR A5

The UE may send measurement reports such that:cell_x1 with RSRP_x for measId x (such that RSRP_x≥RSRPthresh)cell_y1 with RSRP_y for measId y (such that RSRP_y≥RSRPthresh)cell_z1 with RSRP_z for measId z (such that RSRP_z≤RSRPthresh)

In the above situation, RSRP_x, RSRP_y, or RSRP_z may simply be the latest or most recent connection criteria from the MRs; in other configurations they may correspond to values or weighted averages of those values taken over the last time period T or taken over a number N of recent measurements reports. If it is assumed that rsrp_y>rsrp_x>rsrp_z, UE can prioritize cell_y1, followed by cell_x1 before using ACQ DB and during cell selection after an RLF. Cell_z1 would not be prioritized because it does not meet the initial RSRPthreshvalue.

In another configuration below, the UE is considered to have the following connected measurement configuration from the network, as shown in measurement report ranking entries606(FIG.6):1. MeasId x for MeasObj ID x and reportConfig ID x for MR A32. MeasId y for MeasObj ID y and reportConfig ID y for MR A43. MeasId z for MeasObj ID z and reportConfig ID z for MR A5

The UE may send measurement reports such that:cell_x1 with RSRP_x for measId x (such that RSRP_x<RSRPthresh)cell_y1 with RSRP_y for measId y (such that RSRP_y≥RSRPthresh)cell_z1 with RSRP_z for measId z (such that RSRP_z≥RSRPthresh)

Unlike the above example, in this case the UE can use optimized RLF recovery on preferred cells reported in the measurement reports. It should be noted that while entries606may come from prioritization of the measurement report, in some configurations the entries604may be internal information in a UE database tracking the cells and their preferred features.

In the above situation, the connection criteria RSRP_x, RSRP_y, or RSRP_z may also be absolute values or weighted averages taken over the last T time window or N number of measurements reports, as before. If it is now assumed that rsrp_y>rsrp_z>rsrp_x, UE can prioritize cell_z1, followed by cell_y1 before using ACQ DB and during cell selection after an RLF. In this case, cell_x1 would not be prioritized because it does not meet the initial RSRPthreshvalue. The use of preferred features herein may also be influenced by carrier preference, such as in this case, a preference may be mandated by the carrier or standard for use of HST versus ENDC.

Benefits of the above procedure include the ability to identify and prioritize the candidate cells that are reported in Measurement Reports (MRs) during cell selection for RLF recovery, with the knowledge that the UE has been detecting and measuring those same cells in the recent past. In addition, many times when RLF occurs as a result of Handover messages not properly reaching the UE on time due to degraded channel conditions after UE has sent the MR, the proposed solution allows the UE as part of RLF recovery to select the cell to which the network would have most likely handed over the UE. Thus, selecting the cell that is the handover target on a RLF event can be a significant advantage both in time savings and communication quality. These ideas, as noted, need not be specific to one RAT and instead can have equal applicability to 2G/3G/4G/5G, and to future technologies.

FIG.7is a flowchart700of wireless communication. The steps inFIG.7can be performed, for example, by the UE104ofFIG.1(e.g., using component198), the UE350inFIG.3, the UE504inFIG.5, and the apparatus1002inFIG.10. At702, the UE performs connected mode measurements and triggers measurement reports (MRs). At704, as the UE performs the measurements in702, the UE can maintain a database (e.g., an MR Cell DB) of cells reported in measurement reports (including, for example, A3/A4/A5/periodic) ranked by signal strength. At706, it is assumed that a connection is interrupted by an RLF trigger and the connection is lost. At708, the UE thereupon undergoes cell selection for RLF recovery purposes. In this configuration, however, in lieu of accessing the ACQ DB, the UE at710scans frequencies from the above-described MR Cell DB starting with the strongest candidate cell to prioritize the order of candidate cells and find a suitable cell for camping. If a suitable cell is found with adequate levels of signal power, then without further delay, the UE at714can immediately trigger an RRC connection reestablishment request.

By contrast, if at712a suitable cell is not found (such as none of the prioritized candidate cells in the MRs turn out to be workable here), then control moves to A (FIG.7). A in this case simply means that the ordinary cell selection procedures take effect. At716, the UE may proceed to scan frequencies from the ACQ DB to find a suitable cell for camping. A similar procedure at718follows as the UE queries whether a suitable cell is found based on the scanned measurements in the ACQ DB. If a suitable cell is found, then at714the UE can proceed to trigger an RRC Connection reestablishment request and the connection can be restored. Otherwise, if scanning of the ACQ does not yield a suitable candidate cell in718, the UE may trigger a band scan to identify frequencies to perform cell selection. If no eligible candidate frequencies are available in722, the UE may repeat the band scan720, in some case for however often as necessary. Once candidate frequencies are finally identified in722, the UE can scan frequencies from the band scan results to find a suitable cell associated therewith, as in724. Control returns to718, wherein once a suitable cell is found, the UE can trigger the RRC Connection Reestablishment request at714. It should be noted that, if during the band scan720the UE happens to receive connection criteria relating to a candidate cell, through a measurement report or otherwise, the band scan720can be interrupted and the candidate cell analyzed further.

The above example takes into account the signal strength data in the measurement reports (or derivatives therefrom) as corresponding to the connection criteria. In the example below, in addition to the signal strength data, the UE may factor into its prioritization whether the identified cells are compatible with preferred features in use or requested for use by the UE.

FIG.8is a flowchart800of wireless communication. The steps inFIG.8can be performed, for example, by the UE104ofFIG.1(e.g., using component198), the UE350inFIG.3, the UE504inFIG.5, and the apparatus1002inFIG.10.

Referring initially to814, the UE may maintain a database, such as a Preferred Cell DB, identifying cells and their supported features like HST, ENDC, CSG, eMBMS, etc., that the UE has determined from system information blocks (SIBs) during prior camping on those cells. At802, the UE may perform measurements while in Connected mode and may trigger resulting Measurement Reports (MR) to be received at the UE. At804, the UE also maintains an MR Cell DB of cells reported in the various measurement reports, ranked by signal strength in this example. Thus, in this configuration, both cell quality and the presence or absence of preferred features are mutually taken into account and can both be connection criteria used to prioritize candidate cells.

Referring still toFIG.8, it is assumed at806that, during a connection, the UE experiences an RLF trigger. The UE initiates cell selection for RLF recovery at808. In this implementation, however the UE performs cell prioritization by scanning frequencies that have preferred cells from the Preferred Cell DB such that the cells are also found in MR Cell DB with a signal strength greater than some predefined threshold. The UE uses this information to prioritize the candidate cells with preferred features to find a suitable cell for camping and to thereupon select the candidate cell having the highest priority (e.g., the collective best feature(s) and signal quality).

Upon prioritizing the cells as in810, the UE determines whether a suitable cell is found at812. If so, the UE can immediately trigger an RRC Connection Reestablishment request at820, and thereafter restore the connection using the new cell. It is noted that in this case, since the UE had been soliciting MRs earlier in the vicinity (see814), there is a reasonable possibility that an existing MR has identified an ideal cell in the area. The present disclosure enables the UE to find the cell and to do so with great speed. The prioritization technique also enables the UE to immediately drop from consideration otherwise “preferred” candidate cells that are not strong physical candidates for reconnection because they may not meet, or barely meet, a strength threshold (e.g., RSRPthresh).

Referring back to812, control passes to B if a suitable cell is not found at that point. At816, the UE may proceed to scan frequencies from the MR Cell DB starting with the strongest cell to find a suitable cell for camping. In this prioritization, the UE has effectively “cast a wider net” by not limiting the search for cells with preferred features, but rather by searching for strong cells that would facilitate a fast reconnection. At818, the UE may again query whether a suitable cell has been found. If so, then control may return again to820, in which event the UE may issue an RRC connection reestablishment request. Thus the UE can restore the connection using a strong cell, albeit without necessarily the same preferred features, and the UE can do so with a low latency since it has not yet been required to scan the ACQ DB.

If, by contrast, a suitable cell still has not been found at this point, control goes to A, which means that in this configuration, the UE can still fall back on conventional techniques for restoring the connection. At822, the UE may proceed to scan frequencies from the ACQ DB to find a suitable cell for camping. At824, if such a cell is found, the UE can issue an RRC reestablishment request (at820). Otherwise, at826, the UE can trigger a band scan to identify frequencies to perform cell selection. If candidate frequencies at828are identified, the UE may scan the frequencies at830to find a suitable cell, and the cycle repeats at824. If candidate frequencies at828are not yet identified, the UE can resume the band scan at826.

Thus a worst case scenario as in the above examples is where the UE scans the measurement reports and, based on the connection criteria or on the absence of cells, the UE does not find a viable candidate cell. Overall, however, this process is both likely to yield beneficial results given the constantly updated nature of the measurement reports (which can yield alternatives), and which is not too time consuming because it does not require access to the ACQ DB. If all else fails, as noted above, the conventional techniques for finding a suitable cell always remain an option for the UE meaning that overall, chances of reestablishing a connection and restoring the link after the RLF may be increased.

FIG.9is another flowchart900for wireless communication. LikeFIGS.7and8, the steps inFIG.9may be performed, for example, by the UE104ofFIG.1(e.g., using component198), the UE350inFIG.3, the UE504inFIG.5, and the apparatus1002inFIG.10.FIG.9takes the constituent steps described with respect toFIGS.7and8and rewrite them in a more general form. At902, the UE identifies an RLF of an existing wireless connection. It may be sufficient, for example, that the connection simply drops and the link is terminated. During the ensuing RLF recovery for restoring the connection, the UE may prioritize candidate cells using connection criteria from specific measurement reports. These connection criteria may include values indicative of signal strength, signal to noise ratio, and the nature or quality of channel conditions in general. For example, as previously discussed, one such connection criterion may be a minimum threshold for consideration, such as RSRPthresh, to ensure that weak cells are not involved in the prioritization.

Other connection criteria include, for example, values of RSRP, RSRQ, and other measurements from one or more MRs. The connection criteria may be taken as is, or the numbers may be taken over several most recent MRs in the memory of the UE at the time of RLF. For example, the connection criteria need not just be absolute values, but may be weighted or averaged values measured over some period of time T, or measured using some number of previous MRs. Connection criteria from B1and B2may be used for forwarding information to specific RATs for subsequent use, and need not necessarily be used for restoring the dropped connection. The connection criteria can be computed quickly and then can be used to prioritize the candidate cells. Connection criteria indicative of a strong connection are typically associated with cells having a higher priority. In configurations where preferred features are taken into account as discussed at length above, the connection criteria may also include the identity of these features, and, if appropriate, a value assigned to a relative importance of these features, depending on factors like their relative importance to the governing standard or to the carrier, whether they were used in the last cell, and other factors. To ensure that weak cells are not considered, connection criteria may also be used to eliminate preferred cells having a strength that does not reach a threshold.

In some configurations, and as seen above with respect toFIGS.7and8, prioritization of candidate cells can be part of an ongoing process. Prioritization may in part occur if, as in step704ofFIG.7or step804ofFIG.8, the UE maintains in connected mode a database of cells reported in various measurement reports and ranks the cells by signal strength. This preexisting activity of maintaining an existing repository of prioritized cells may serve to speed up recovery from the RLF. If priority data is already stored, for example, then the prioritizing procedure upon identifying an RLF event can be increased in speed. Prioritization after RLF may just require updating the rankings based on the location of the failure, or augment or modify the existing ranking to incorporate new events. In some configurations, the prioritizing after RLF can involve taking preexisting determinations to the extent possible, and identifying the list of candidate cells based on those preexisting determinations, albeit with any necessary updates or modifications (e.g., to take an average of measurements) performed where necessary.

At906, the UE may take action to restore the connection using a cell having the highest priority per the connection criteria. For example, if HST is a feature deemed valuable in the context of the UE and the UE finds a cell having high RSRP and RSRQ values, as well as HST capability, these connection criteria may place this identified cell at the top of the ranking. In one configuration, the remaining cells are ranked accordingly and preserved in the memory of the UE in the event of another RLF, or in the event the highest priority cell cannot be used to restore the connection.

The connection may be restored using an RRC Connection reestablishment request, although in other wireless technologies or circumstances, alternatives are possible for restoring the connection using the highest priority cell.

FIG.10is a diagram1000illustrating an example of a hardware implementation for an apparatus1002. The apparatus1002is a UE and includes one or more cellular baseband processors1004(also referred to as a modem) coupled to a cellular RF transceiver1022and one or more subscriber identity modules (SIM) cards1020, an application processor1006coupled to a secure digital (SD) card1008and a screen1010, a Bluetooth module1012, a wireless local area network (WLAN) module1014, a Global Positioning System (GPS) module1016, and a power supply1018. The one or more cellular baseband processors1004communicate through the cellular RF transceiver1022with the UE104and/or BS102/180. The one or more cellular baseband processors1004may each include a computer-readable medium/one or more memories. The computer-readable medium/one or more memories may be non-transitory. The one or more cellular baseband processors1004are responsible for general processing, including the execution of software stored on the computer-readable medium/one or more memories individually or in combination. The software, when executed by the one or more cellular baseband processors1004, causes the one or more cellular baseband processors1004to, individually or in combination, perform the various functions described supra. The computer-readable medium/one or more memories may also be used individually or in combination for storing data that is manipulated by the one or more cellular baseband processors1004when executing software. The one or more cellular baseband processors1004individually or in combination further include a reception component1030, a communication manager1032, and a transmission component1034. The communication manager1032includes the one or more illustrated components. The components within the communication manager1032may be stored in the computer-readable medium/one or more memories and/or configured as hardware within the one or more cellular baseband processors1004.

In the context ofFIG.3, the one or more cellular baseband processors1004may be components of the UE350and may individually or in combination include the one or more memories360and/or at least one of the one or more TX processors368, at least one of the one or more RX processors356, and at least one of the one or more controllers/processors359. In one configuration, the apparatus1002may be a modem chip and include just the one or more baseband processors1004, and in another configuration, the apparatus1002may be the entire UE (e.g., see350ofFIG.3) and include the aforediscussed additional modules of the apparatus1002. In one configuration, the cellular RF transceiver1022may be implemented as at least one of the transmitter354TX and/or the receiver354RX.

The communication manager1032includes an ACQ DB component1040that is configured to provide a list of one or more frequencies corresponding to cells that the UE was recently camped on, e.g., as described in connection with step716inFIG.7and step822inFIG.8. The communication manager1032further includes a measurement report component1042that receives input in the form of UE measurement requests performed in connected mode from one or more components and is configured to provide resulting measurement data to an MR Cell DB, e.g., as described in connection with steps702and704ofFIG.7and steps802and804ofFIG.8. The communication manager1032further includes a Preferred Cell DB component1044that receives input in the form of supported features determined from SIBs while the UE previously camped on other cells and is configured to submit the identified features to the Cell Prioritizing Component1050, e.g., as described in connection with steps810and814inFIG.8. The communication manager1032also includes an RLF Identifying Component1046that receives input indicative of a radio link failure from receiving component1030and that is configured to initiate a restoring action to restore the failed link, as shown in steps706and708fromFIG.7, steps806and808fromFIG.8, and steps902and904fromFIG.9.

The communication manager1032also includes an RRC Reestablishment Component1046that receives input in the form of candidate cells from cell prioritizing component1050and that is configured to issue an RRC Reestablishment request upon receiving data corresponding to a suitable cell, as shown in steps714and718ofFIG.7, steps812and820ofFIG.8, and step906ofFIG.9. The communication manager1032also includes a Cell Prioritizing Component1050that receives input in the form of measurement data from measurement report component1042and preferred cell DB component1044and that is configured to prioritize the candidate cells as shown in step904ofFIG.9, steps704and710ofFIG.7, and steps804,810,814, and816ofFIG.8.

The apparatus1002may include additional components that perform some or all of the blocks, operations, signaling, etc. of the algorithm(s) in the aforementioned flowchart(s) ofFIGS.7-9. As such, some or all of the blocks, operations, signaling, etc. in the aforementioned flowchart(s) ofFIGS.7-9may be performed by a component and the apparatus1002may include one or more of those components. The components may be one or more hardware components specifically configured to carry out the stated processes/algorithm, implemented by one or more processors individually or in combination configured to perform the stated processes/algorithm, stored within a computer-readable medium for implementation by one or more processors, or some combination thereof.

In one configuration, the apparatus1002, and in particular the one or more cellular baseband processors1004, includes means for identifying a radio link failure (RLF) of an existing wireless connection; means for prioritizing, during an RLF recovery procedure for restoring the connection, candidate cells using connection criteria from one or more measurement reports; and means for restoring the connection using the candidate cell having a highest priority.

The aforementioned means may be one or more of the aforementioned components of the apparatus1002configured to perform the functions recited by the aforementioned means. As described supra, the apparatus1002may include the one or more TX Processors368, the one or more RX Processors356, and the one or more controllers/processors359. As such, in one configuration, the aforementioned means may be at least one of the one or more TX Processors368, at least one of the one or more RX Processors356, or at least one of the one or more controllers/processors359, individually or in any combination configured to perform the functions recited by the aforementioned means.

Aspects of the present disclosure provide optimal cell selection during RLF recovery. As noted above, when RLF occurs in Connected mode, the UE generally performs cell selection to recover from RLF and performs an RRC Connection Reestablishment procedure upon selecting a cell. As part of the conventional cell selection procedure for RLF recovery, the UE may scan the last camped cells identified in the UE's ACQ DB. When none of the cells in the ACQ DB are suitable for cell selection in conventional approaches, UE may resort to time-intensive frequency band scanning to identify a suitable cell. In this case, overall RLF recovery may be delayed. Another shortcoming of existing solutions involves the case where the UE finds a suitable cell during the course of RLF recovery that the UE determines not to be a preferred cell. For example, the UE performing the cell selection may support HST as a preferred node. The UE may spend initial time searching for cells that do not support this feature. In such case, the UE may take an even longer time to identify a preferred cell, which may further delay the overall process to return to a connected state.

In other cases, referring still to the example where the UE has HST in its preferred cell list, RLF recovery may be attempted via non-HST ACQ DB cells in spite of the fact that an A4measurement report, for example, may identify an HST cell having a stronger signal strength. Accordingly, in these conventional systems, the UE may forego consideration of the HST cell even where the UE includes HST capability for cells in measurement reports with favorable conditions. In addition to the delay associated with the longer cell selection period, the resulting cell selected conventionally may provide a lower throughput, in some cases substantially lower, than the HST cell identified in the A4measurement report.

Accordingly, to avoid the possibility of sub-optimal performance identified in the example above, when a UE encounters RLF and consequently initiates cell selection, prioritization of cells may be performed on preferred cells. Prioritizing cell selection in this manner may avoid the problem where none of the cells in the ACQ DB are strong enough in the geographical location where the RLF occurred, and the UE may be triggering a time-consuming band scan to find a suitable cell in lieu of trying to recover quickly on stronger cells reported in Measurement reports. In addition, a UE preferring an HST cell may not be able to perform RLF recovery on an HST cell. As another example, a UE preferring an LTE anchor cell (supporting LTE-NR ENDC) may be performing RLF recovery on a non-anchor LTE cell. The principles in this disclosure provide solutions for these shortcomings.

In another examples, cell selection may benefit substantially where any one or more of A3, A4, A5, inter-RAT measurement reports, or periodic measurement reports are initially identified and one or more connection criteria, such as RSRP, RSRQ, or other listed criteria are used to determine cell quality. In these cases, strong cells can be identified in short time periods that have the attributes necessary for reestablishing a high quality connection.

In other configurations, during cell selection where applicable, the preferred cell features, which may include any UE-desirable features identified in a governing standard or specified by a wireless carrier, may be given initial priority such that cells corresponding to the preferred features are searched before other cells during the measurement reports. In this manner, reconnection can be established very quickly using preferred features without the time delays that are conventionally associated with exhausting the UE's ACQ DB, and thereafter (where necessary) incurring further delay with a band scan. Instead, if the cell corresponding to the preferred features has sufficient signal power or otherwise is sufficient under network conditions, the cell having the standardized feature or the carrier-specified feature can be obtained directly from one of the measurement report such that a connection that continues use of the preferred feature can be selected quickly.

As used herein, a processor, at least one processor, and/or one or more processors, individually or in combination, configured to perform or operable for performing a plurality of actions (such as the functions described supra) is meant to include at least two different processors able to perform different, overlapping or non-overlapping subsets of the plurality actions, or a single processor able to perform all of the plurality of actions. In one non-limiting example of multiple processors being able to perform different ones of the plurality of actions in combination, a description of a processor, at least one processor, and/or one or more processors configured or operable to perform actions X, Y, and Z may include at least a first processor configured or operable to perform a first subset of X, Y, and Z (e.g., to perform X) and at least a second processor configured or operable to perform a second subset of X, Y, and Z (e.g., to perform Y and Z). Alternatively, a first processor, a second processor, and a third processor may be respectively configured or operable to perform a respective one of actions X, Y, and Z. It should be understood that any combination of one or more processors each may be configured or operable to perform any one or any combination of a plurality of actions.

Similarly as used herein, a memory, at least one memory, a computer-readable medium, and/or one or more memories, individually or in combination, configured to store or having stored thereon instructions executable by one or more processors for performing a plurality of actions (such as the functions described supra) is meant to include at least two different memories able to store different, overlapping or non-overlapping subsets of the instructions for performing different, overlapping or non-overlapping subsets of the plurality actions, or a single memory able to store the instructions for performing all of the plurality of actions. In one non-limiting example of one or more memories, individually or in combination, being able to store different subsets of the instructions for performing different ones of the plurality of actions, a description of a memory, at least one memory, a computer-readable medium, and/or one or more memories configured or operable to store or having stored thereon instructions for performing actions X, Y, and Z may include at least a first memory configured or operable to store or having stored thereon a first subset of instructions for performing a first subset of X, Y, and Z (e.g., instructions to perform X) and at least a second memory configured or operable to store or having stored thereon a second subset of instructions for performing a second subset of X, Y, and Z (e.g., instructions to perform Y and Z). Alternatively, a first memory, a second memory, and a third memory may be respectively configured to store or have stored thereon a respective one of a first subset of instructions for performing X, a second subset of instruction for performing Y, and a third subset of instructions for performing Z. It should be understood that any combination of one or more memories each may be configured or operable to store or have stored thereon any one or any combination of instructions executable by one or more processors to perform any one or any combination of a plurality of actions. Moreover, one or more processors may each be coupled to at least one of the one or more memories and configured or operable to execute the instructions to perform the plurality of actions. For instance, in the above non-limiting example of the different subset of instructions for performing actions X, Y, and Z, a first processor may be coupled to a first memory storing instructions for performing action X, and at least a second processor may be coupled to at least a second memory storing instructions for performing actions Y and Z, and the first processor and the second processor may, in combination, execute the respective subset of instructions to accomplish performing actions X, Y, and Z. Alternatively, three processors may access one of three different memories each storing one of instructions for performing X, Y, or Z, and the three processors may in combination execute the respective subset of instruction to accomplish performing actions X, Y, and Z. Alternatively, a single processor may execute the instructions stored on a single memory, or distributed across multiple memories, to accomplish performing actions X, Y, and Z.

Example 1 is a method for wireless communication at a user equipment (UE), comprising identifying a radio link failure (RLF) of an existing wireless connection, prioritizing, during an RLF recovery procedure for restoring the connection, candidate cells using connection criteria from one or more measurement reports; and restoring the connection using the candidate cell having a highest priority.

Example 2 is the method of example 1, wherein the one or more measurement reports comprises at least one of A3, A4, A5, periodic, or inter-RAT measurement reports.

Example 3 is the method of any of Examples 1 and 2, method of claim1, wherein restoring the connection comprises identifying the highest priority cell to a base station during a radio resource control (RRC) connection reestablishment.

Example 4 is the method of any of Examples 1 to 3, wherein prioritizing the candidate cells using the connection criteria comprises comparing reference signal received powers (RSRP) values corresponding to each of the candidate cells.

Example 5 is the method of any of Examples 1 to 4, wherein prioritizing the candidate cells using the connection criteria comprises comparing reference signal received qualities (RSRQ) values corresponding to each of the candidate cells.

Example 6 is the method of any of Examples 1 to 5, wherein prioritizing the candidate cells using the connection criteria further includes comparing average connection criteria over a time period, or a number of recent reports.

Example 7 is the method of any of Examples 1 to 6, wherein prioritizing the candidate cells using the connection criteria further includes comparing only the candidate cells that satisfy a minimum connection quality threshold.

Example 8 is the method of any of Examples 1 to 7, further comprising updating prioritizing of the candidate cells when an updated one or more measurement reports are received.

Example 9 is the method of any of Examples 1 to 8, wherein prioritizing the candidate cells using the connection criteria further comprises updating cells with more recently reported cells for a same type of reporting event,

Example 10 is the method of any of Examples 1 to 9, further comprising: identifying cells reported in B1or B2reports; reporting the cells to a base station using a target radio access technology (RAT); and using one of the reported cells during cell selection when needed for the target RAT.

Example 11 is the method of any of Examples 1 to 10, further comprising maintaining a prioritized list of the candidate cells during a radio resource control (RRC) connection until the UE returns to idle.

Example 12 is the method of any of Examples 1 to 11, wherein prioritizing the candidate cells using the connection criteria further comprises giving initial priority to cells in the one or more measurement reports that are included in a preferred cell database corresponding to a preferred feature supported by the UE.

Example 13 is the method of any of Examples 1 to 12, wherein prioritizing the candidate cells using the connection criteria further comprises giving initial priority to cells in the one or more measurement reports that are included in a preferred cell database corresponding to a preferred feature supported by the UE.

Example 14 is the method of any of Examples 1 to 13, further comprising giving the initial priority to cells from the one or more measurement reports that are included in the preferred cell database only for the cells that satisfy a minimum connection quality threshold.

Example 14 is an apparatus including one or more memories; and one or more processors each communicatively coupled with at least one of the one or more memories, the one or more processors, individually or in any combination, operable to cause the apparatus to: perform any of the steps of Examples 1 to 14.

Example 15 is one or more non-transitory computer-readable media comprising computer-executable code, the code when executed by one or more processors causes the one or more processors to, individually or in combination, perform any of the steps of Examples 1 to 14.

Example 16 is an apparatus including means for performing any of the functions of Examples 1-14.