Patent Description:
There exists a need for further improvements in <NUM> NR technology, including a need for improved cell selection/reselection.

<CIT>, relates to a method and system for facilitating cell selection, cell reselection, cell change order and/or handover of a mobile terminal between digital cellular networks having heterogeneous Radio Access Technologies. <CIT>, relates to adjusting reselection thresholds based on inter-radio access technology (IRAT) neighbor measurements and inter-frequency neighbor measurements. <CIT>, relates to systems and methods for inter-radio access technology (inter-RAT) reselection.

Preferred embodiments are defined by the appended dependent claims.

A radio access technology (RAT) is the underlying physical connection method for a radio based communication network. A UE may support several RATs such as <NUM>, <NUM>, <NUM>, and <NUM>, and may switch between the different RATs based on the type of RAT supported by a serving cell. A cell reselection procedure is a mechanism by which an IDLE mode UE may reselect from a serving cell to a neighbor cell. An inter-RAT (IRAT) cell reselection is a procedure by which a UE may reselect from a serving cell that supports a first type of RAT to a neighbor cell associated that supports a second type of RAT.

Cell reselection and/or IRAT cell reselection may enable a UE to connect to a neighbor cell that has an increased quality of service (e.g., a higher data rate) as compared to the serving cell. One type of cell reselection procedure is a rank-based reselection procedure. Another type of cell reselection procedure is a priority-based reselection procedure.

When rank-based reselection is enabled, information that is used to perform a rank-based reselection procedure may be communicated to the UE via a system information block (SIB). The information in the SIB may include, e.g., reselection threshold criteria used to determine whether to measure the signal strength of neighbor cells, parameters used for calculating the respective ranks of the serving cell and neighbor cells, etc..

Periodically (e.g., at the end of a discontinuous reception (DRX) cycle), the UE may measure a signal strength of the serving base station. When the signal strength of the serving cell meets the reselection threshold criteria, the UE may determine the rank of the serving cell and each of the neighbor cells based on the information received in the SIB, and may reselect to the cell with the highest rank. Due to the complexity of the signal strength measurements and the reselection threshold criteria, performing a rank-based reselection procedure may consume an undesirable amount of battery power and/or reduce the quality of service.

A priority-based reselection procedure may enable the UE to reselect to a neighbor cell that has a higher priority RAT than the serving cell. For example, <NUM> NR may be the highest priority RAT, <NUM> may be the second highest priority RAT, <NUM> may be the third highest priority RAT, and so on.

When priority-based cell reselection is enabled, information (e.g., a reselection priority list) used to perform the priority-based cell reselection procedure may be communicated to the UE via an SIB. The reselection priority list may prioritize one or more different radio frequencies of neighbor cells operating on a highest priority RAT. Hence, when a UE with a <NUM> subscriber identification module (SIM) card is camped on a <NUM> serving cell, the reselection priority list may include a prioritized list of radio frequencies associated with one or more <NUM> neighbor cells but not the radio frequencies of <NUM> neighbor cells. The radio frequencies may be prioritized based on system overhead, data rate, etc..

However, when <NUM> services are inaccessible to the UE or when the <NUM> neighbor cells are barred, the UE may be forced to reselect to a <NUM> neighbor cell instead of a <NUM> neighbor cell even though <NUM> services are accessible to the UE (e.g., because the reselection priority list did not include radio frequencies for <NUM> neighbor cells). Thus, there is a need for a cell reselection mechanism that enables a UE to reselect to the highest priority RAT accessible to the UE when the reselection priority list does not include the radio frequencies for a preferred RAT.

The present disclosure provides a solution to the problem by enabling the UE to perform a rank-based reselection procedure when the UE is unable to reselect to the RAT indicated in the radio frequencies of the reselection priority list.

The wireless communications system (also referred to as a wireless wide area network (WWAN)) includes base stations <NUM>, UEs <NUM>, an Evolved Packet Core (EPC) <NUM>, and a second Core network <NUM>, such as a <NUM> core network.

The base stations <NUM> configured for <NUM> LTE (collectively referred to as Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (E-UTRAN)) may interface with the EPC <NUM> through backhaul links <NUM> (e.g., S1 interface). The base stations <NUM> configured for <NUM> NR (collectively referred to as Next Generation RAN (NG-RAN)) may interface with core network <NUM> through backhaul links <NUM>. The base stations <NUM> may communicate directly or indirectly (e.g., through the EPC <NUM> or core network <NUM>) with each other over backhaul links <NUM> (e.g., X2 interface).

A network that includes both small cell and macro cells may be known as a heterogeneous network. The base stations <NUM> / UEs <NUM> may use spectrum up to YMHz (e.g., <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, etc. MHz) bandwidth per carrier allocated in a carrier aggregation of up to a total of Yx MHz (x component carriers) used for transmission in each direction. Allocation of carriers may be asymmetric with respect to DL and UL (e.g., more or less carriers may be allocated for DL than for UL).

D2D communication may be through a variety of wireless D2D communications systems, such as for example, FlashLinQ, WiMedia, Bluetooth, ZigBee, Wi-Fi based on the Institute of Electrical and Electronics Engineers (IEEE) <NUM> standard, LTE, or NR.

A base station <NUM>, whether a small cell <NUM>' or a large cell (e.g., macro base station), may include an eNB, gNodeB (gNB), or other type of base station. Extremely high frequency (EHF) is part of the radio frequency (RF) band in the electromagnetic spectrum. Communications using the mmW / near mmW radio frequency band has high path loss and a short range. The mmW base station <NUM> may utilize beamforming <NUM> with the UE <NUM> to compensate for the high path loss and short range.

The base station <NUM> may transmit a UE-bound beamformed signal to the UE <NUM> in one or more transmit directions <NUM>'. The UE <NUM> may receive the UE-bound beamformed signal from the base station <NUM> in one or more receive directions <NUM>". The UE <NUM> may also transmit a BS-bound beamformed signal to the base station <NUM> in one or more transmit directions. The base station <NUM> may receive the BS-bound beamformed signal from the UE <NUM> in one or more receive directions. The transmit and receive directions determined by beam training for the base station <NUM> may or may not be the same. The transmit and receive directions determined by beam training for the UE <NUM> may or may not be the same.

The IP Services <NUM> may include the Internet, an intranet, an IP Multimedia Subsystem (IMS), a Streaming Service, and/or other IP services.

The core network <NUM> may include a Access and Mobility Management Function (AMF) <NUM>, a Session Management Function (SMF) <NUM>, and a User Plane Function (UPF) <NUM>.

Referring again to <FIG>, in certain aspects, the UE <NUM> may be configured to switch from a priority-based reselection mechanism, e.g., based on a priority list, to a rank-based reselection mechanism, e.g., based on a measured signal strength, when the UE <NUM> is unable to reselect to a RAT indicated in a reselection priority list (<NUM>), e.g., as described below in connection with any of <FIG>.

The <NUM>/NR frame structure may be frequency division duplex (FDD) in which for a particular set of subcarriers (carrier system bandwidth), subframes within the set of subcarriers are dedicated for either DL or UL, or may be time division duplex (TDD) in which for a particular set of subcarriers (carrier system bandwidth), subframes within the set of subcarriers are dedicated for both DL and UL. In the examples provided by <FIG>, the <NUM>/NR frame structure is illustrated as being TDD, with subframe <NUM> being configured with slot format <NUM> (with mostly DL), where D is DL, U is UL, and X is flexible for use between DL/UL, and subframe <NUM> being configured with slot format <NUM> (with mostly UL).

The symbols on DL may be cyclic prefix (CP) orthogonal frequency division multiplexing (OFDM) (CP-OFDM) symbols. The subcarrier spacing may be equal to <NUM>µ * <NUM> kKz, where µ is the numerology <NUM> to <NUM>.

As illustrated in <FIG>, some of the REs carry reference signals (RSs) for the UE (sometimes also referred to a pilot signals). The RSs may include demodulation RS (DM-RS) (indicated as Rx for one particular configuration, where 100x is the port number, but other DM-RS configurations are possible) and channel state information reference signals (CSI-RS) for channel estimation at the UE. The RSs may also include beam measurement RS (BMRS), beam refinement RS (BRRS), and phase tracking RS (PT-RS).

A RAT is the underlying physical connection method for a radio-based communication network. UEs may support several RATs such as <NUM>, <NUM>, <NUM>, and <NUM>, and may switch between the different RATs based on the type of RAT supported by a serving cell. A cell reselection procedure is a mechanism by which an IDLE mode UE may reselect from a serving cell to a neighbor cell. An IRAT cell reselection is a procedure by which a UE may reselect from a serving cell that supports a first type of RAT to a neighbor cell associated that supports a second type of RAT.

When rank-based reselection is enabled, information that is used to perform a rank-based reselection procedure may be communicated to the UE via an SIB. The information in the SIB may include, e.g., reselection threshold criteria used to determine whether to measure the signal strength of neighbor cells, parameters used for calculating the respective ranks of the serving cell and neighbor cells, etc..

Periodically (e.g., at the end of a DRX cycle), the UE may measure a signal strength of the serving base station. When the signal strength of the serving cell meets the reselection threshold criteria, the UE may determine the rank of the serving cell and each of the neighbor cells based on the information received in the SIB, and reselect to the cell with the highest rank. Due to the complexity of the signal strength measurements and the reselection threshold criteria, performing a rank-based reselection procedure may consume an undesirable amount of battery power and/or reduce the quality of service.

When priority-based cell reselection is enabled, information (e.g., a reselection priority list) used to perform the priority-based cell reselection procedure may be communicated to the UE via a SIB. The reselection priority list may prioritize one or more different radio frequencies associated with neighbor cells operating on the highest priority RAT. Hence, when a UE with a <NUM> SIM card is camped on a <NUM> serving cell, the reselection priority list may include a prioritized list radio frequencies associated with one or more <NUM> neighbor cells but not the radio frequencies of <NUM> neighbor cells. The radio frequencies may be prioritized based on system overhead, data rate, etc..

<FIG> and <FIG> illustrate a data flow <NUM> that may be used to switch from a priority-based reselection mechanism to a rank-based reselection mechanism when a UE is unable to reselect to a RAT indicated in a reselection priority list in accordance with certain aspects of the disclosure. In certain implementations, the data flow <NUM> may enable the UE <NUM> to reselect from the serving base station <NUM> (e.g., serving cell) to one of a first neighbor base station <NUM> operating on a first RAT, a second neighbor base station <NUM> operating on a second RAT, and/or a third neighbor base station <NUM> operating on a third RAT. At least one of the first, second, and/or third RATs may the same as the RAT on which the serving base station operates.

The UE <NUM> may correspond to, e.g., the UE <NUM>, <NUM>, the apparatus <NUM>/<NUM>'. The serving base station <NUM> may correspond to, e.g., the base station <NUM>, <NUM>, <NUM>, the serving base station <NUM>. The first neighbor base station <NUM> may correspond to, e.g., the base station <NUM>, <NUM>, <NUM>, neighbor base station <NUM>. The second neighbor base station <NUM> may correspond to, e.g., the base station <NUM>, <NUM>, <NUM>, neighbor base station <NUM>. The third neighbor base station <NUM> may correspond to, e.g., the base station <NUM>, <NUM>, <NUM>. In <FIG> and <FIG>, optional operations are indicated with dashed lines.

Referring to <FIG>, the UE <NUM> may receive (at <NUM>) a reselection priority list associated with preferred radio frequencies from the serving base station <NUM>. In certain aspects, each radio frequency of the preferred radio frequencies is associated with a first set of base stations operating on a first RAT. In certain other aspects, the first RAT may be the highest priority RAT associated with the UE <NUM>. For example, <NUM> NR may be the highest priority RAT, <NUM> may be the second highest priority RAT, <NUM> may be the third highest priority RAT, and so on. Hence, when the UE <NUM> has a <NUM> SIM card, <NUM> may be highest priority RAT associated with the UE <NUM>. However, when the UE <NUM> has a <NUM> SIM card and not a <NUM> SIM card, <NUM> may be the highest priority RAT associated with the UE <NUM>, and so on. In the example illustrated in <FIG> and <FIG>, the first set of neighbor base stations may include the first neighbor base station <NUM>.

The UE <NUM> may use the reselection priority list to scan for a base station to reselect to and/or acquire when the UE <NUM> performs a power-up, or in response to a radio link failure.

In certain configurations, the UE <NUM> may determine (at <NUM>) whether the UE is able to reselect to the first RAT (e.g., the first neighbor base station <NUM>). For example, the UE <NUM> may determine (at <NUM>) that the UE <NUM> is able to reselect to the first RAT when the UE <NUM> is subscribed for first RAT services and when the neighbor cells operating on the first RAT are unbarred. Otherwise, the UE <NUM> may determine (at <NUM>) that the UE is unable to reselect to the first RAT when the UE is unsubscribed for first RAT services and/or when the neighbor cells associated with the first RAT are barred.

When the UE <NUM> determines (at <NUM>) that the UE <NUM> is unable to reselect to the first RAT, the operation continues at <NUM> in <FIG>. Otherwise, when the UE <NUM> determines (at <NUM>) that the UE is able to reselect to the first RAT, the operation continues at <NUM> in <FIG>.

Still referring to <FIG>, the UE <NUM> may perform (at <NUM>) a rank-based cell reselection procedure based on signal strength when the UE <NUM> is unable to reselect to the first RAT (e.g., the first neighbor base station <NUM>). Thus, the UE may perform reselection using different mechanisms, e.g., priority-based reselection or rank-based reselection, based on whether the UE is able to reselect to a cell operating on a particular RAT, e.g., a most desired RAT, a same RAT as a serving cell, etc. In certain configurations, the UE <NUM> may perform the rank-based cell reselection procedure by determining (at <NUM>) that a first signal strength associated with the serving base station meets a reselection threshold criteria.

For example, an IDLE mode UE <NUM> may enter a wake mode of every DRX cycle to measure the signal of the serving base station <NUM> (Qmeas,s) and determine (at <NUM>) the received signal level (Srxlev) of the serving base station <NUM>. Based on the received signal level (Srxlev), the UE <NUM> may determine whether to remain camped on the serving cell (e.g., the serving base station <NUM>) or whether to reselect to a neighbor base station. Here, the transmission and reception conditions the UE <NUM> may be reflected in the determination (at <NUM>), for example, by applying minimum received signal level (Qrxlevmin), allowed maximum TX power level PEMAX, etc. If the received signal level (Srxlev) of the serving base station <NUM> is greater than or equal to the specified threshold value (s-IntraSearch), the UE <NUM> may remain camped on the serving cell (e.g., the serving base station <NUM>). Otherwise, the operation may continue to perform rank-based reselection procedure based on signal strength at <NUM>.

In certain other configurations, the UE <NUM> may perform the rank-based reselection procedure by determining (at <NUM>) a respective second signal strength (Qmeas,n) associated with each of a second set of neighbor base stations <NUM>, <NUM> upon determining (at <NUM>) that the first signal strength (Srxlev) meets the reselection threshold criteria (e.g., is less than s-IntraSearch). In certain aspects, the second set of neighbor base stations <NUM>, <NUM>, etc. may be different than the first set of neighbor base stations, e.g., including base station <NUM>.

In certain other configurations, the UE <NUM> may perform the rank-based reselection procedure by ranking (at <NUM>) each neighbor base station <NUM>, <NUM> in the second set of neighbor base stations based on the respective second signal strength for each neighbor base station. For example, the UE <NUM> may rank each cell (Rs, Rn) based on the measured signal strength of the serving cell (Qmeas,s) and neighbor cells (Qmeas,n), where Rs is the rank of the serving cell and Rn is the rank of a particular neighbor cell. Parameters used for cell ranking may be communicated to the UE <NUM> through, e.g., SIBs <NUM> and <NUM> from the serving base station <NUM>. The serving base station <NUM> may be ranked using the hysteresis (q-Hyst) value included in a SIB, e.g., SIB <NUM>, while the neighbor base stations <NUM>, <NUM> may be ranked-based on the offset (q-OffsetCell) value specified for each cell in another SIB, e.g., SIB <NUM>.

Once the serving base station <NUM> and each neighbor base station in the second set of neighbor base stations <NUM>, <NUM> are ranked (at <NUM>), the UE <NUM> may determine if the cell reselection criterion is satisfied (Rn > Rs). Upon determining that one or more neighbor base stations <NUM>, <NUM> satisfy the cell reselection criterion, the UE <NUM> may perform the rank-based reselection procedure by reselecting (at <NUM>) to a highest ranked neighbor base station in the second set of neighbor base stations <NUM>, <NUM>. In certain aspects the highest ranked neighbor base station <NUM> may be operating on a RAT different from the RAT on which the serving base station <NUM> operates. For example, the highest ranked neighbor base station may be operating on a second RAT. The second RAT may be the second highest priority RAT associated with the UE <NUM>. For example, if the UE <NUM> has a <NUM> SIM card but either is unsubscribed for <NUM> services and/or the <NUM> neighbor cell (e.g., first neighbor base station <NUM>) is barred, a selection/reselection to a <NUM> cell would fail. If the UE relies on a priority-based reselection even when selection among cells of the highest priority RAT has failed, the UE may select a less desirable base station. For example, if there are no priorities for <NUM> cells, the UE may select a <NUM> cell even when a <NUM> cell was possible. By using the rank-based reselection mechanism described above, the UE <NUM> may be able to reselect to a more desirable RAT (e.g., second neighbor base station <NUM> associated with the second RAT) instead of reselecting to a base station with a less desirable RAT that has available priority information, e.g., to less desired RAT neighbor base station <NUM>. In certain configurations, the UE <NUM> may perform (at <NUM>) cell acquisition of the second neighbor base station <NUM> operating on the second RAT.

Referring to <FIG>, the UE <NUM> may perform (at <NUM>) a priority-based cell reselection procedure for the first set of neighbor base stations <NUM> when the UE is able to reselect to the first RAT. For example, the UE <NUM> may perform the priority-based cell reselection procedure by reselecting (at <NUM>) to a highest priority base station operating on the preferred radio frequencies that meets a threshold criteria. In one aspect the highest priority base station may be operating on the first RAT. The reselection priority list may prioritize one or more radio frequencies associated with different neighbor cells operating on the highest priority RAT (e.g., a preferred RAT) associated with the UE <NUM>.

Hence, when the UE <NUM> includes a <NUM> SIM card and is camped on a <NUM> serving base station <NUM>, the reselection priority list may include a prioritized list of <NUM> neighbor base station(s) <NUM> but not <NUM> neighbor base station(s) <NUM>. The <NUM> neighbor cells may be prioritized based on system overhead, data rate, etc. The threshold criteria associated with the neighbor base stations prioritized in the reselection priority list may be a minimum signal strength. In other words, the UE <NUM> may reselect to the highest priority neighbor cell included in the list that also meets the minimum signal strength.

In certain configurations, the UE <NUM> may perform (at <NUM>) cell acquisition of the first neighbor base station <NUM> operating on the first RAT when the first neighbor base station <NUM> is the highest priority neighbor base station in the reselection priority list that meets the threshold criteria.

Thus, using the mechanism described above in connection with <FIG> and <FIG>, UE <NUM> may perform a rank-based reselection procedure when the UE is unable to reselect to the RAT indicated in the reselection priority list and when the UE is camped on a less desired RAT (e.g., a cell using <NUM> whereas base stations <NUM>, <NUM> operate using <NUM>). The rank-based reselection may enable the UE to reselect to a neighbor cell operating on a more desirable RAT (e.g., <NUM>nd RAT) associated with the UE <NUM>, rather than to neighbor cell <NUM> operating on a less desirable RAT, even when priority-based reselection would lead the UE to select a cell of the less desirable RAT. The rank-based reselection may be RAT independent so that the UE is able to select among based stations operating using different RATs. In one example, the most desired RAT may be <NUM>, the second most desirable RAT may be <NUM>, and the less desirable RAT may be <NUM>. In another example, the most desirable RAT may be <NUM>, the second most desirable RAT may be <NUM>, and the less desirable RAT may be <NUM>.

<FIG> is a flowchart <NUM> of a method of wireless communication. The method may be performed by a UE (e.g., the UE <NUM>, <NUM>, <NUM>, the apparatus <NUM>/<NUM>'). In <FIG>, optional operations are indicated with dashed lines.

At <NUM>, the UE may receive a priority list associated with preferred radio frequencies from a serving base station. In certain aspects, each radio frequency of the preferred radio frequencies associated with a first set of base stations operating on a first RAT. In certain other aspects, the serving base station may be operating on a RAT that has a lower priority or is less desirable for the UE than the first RAT. For example, referring to <FIG>, the UE <NUM> may receive (at <NUM>) a reselection priority list associated with preferred radio frequencies from the serving base station <NUM>. In the example of <FIG>, the serving base station was operates on a different RAT than the first set of base stations operating on the first RAT. In certain aspects, each radio frequency of the preferred radio frequencies associated with a first set of base station may be associated with a first RAT. In certain other aspects, the first RAT may be the highest priority, most preferred, most recent technology, RAT associated with the UE <NUM>. For example, <NUM> NR may be the preferred RAT, <NUM> may be the next preference for a RAT, <NUM> may be priority less preferred RAT, and so on. Hence, when the UE <NUM> has a <NUM> SIM card, <NUM> may be priority most preferred RAT associated with the UE <NUM>. However, when the UE <NUM> has a <NUM> SIM card and not a <NUM> SIM card, <NUM> may be the most preferred RAT associated with the UE <NUM>, and so on. In the example illustrated in <FIG> and <FIG>, the first set of neighbor base stations may be the first neighbor base station <NUM>.

At <NUM>, the UE may determine if the UE is able to reselect to the first RAT. For example, the UE <NUM> may determine (at <NUM>) whether the UE is able to reselect to the first RAT. For example, the UE <NUM> may determine (at <NUM>) that the UE is able to reselect to the first RAT when the UE is subscribed to first RAT services and when the neighbor cells operating on the first RAT are unbarred. Otherwise, the UE <NUM> may determine (at <NUM>) that the UE is unable to reselect to the first RAT when the UE is unsubscribed for first RAT services and/or when the neighbor cells operating on the first RAT are barred.

Upon determining (at <NUM>) that the UE is unable to reselect to the first RAT, the operation continues at <NUM>. Otherwise, upon determining (at <NUM>) that the UE is able to reselect to the first RAT, the operation continues at <NUM>.

At <NUM>, the UE may perform a rank-based cell reselection procedure based on signal strength when the UE is unable to reselect to the first RAT. For example, referring to <FIG>, the UE <NUM> may perform (at <NUM>) a rank-based cell reselection procedure when the UE <NUM> is unable to reselect to the first RAT. The rank-based reselection may be performed in a RAT independent manner so that the UE may select between base stations operating on different RATs.

At <NUM>, the UE may perform the rank-based cell reselection procedure by determining that a first signal strength associated with the serving base station meets a reselection threshold criteria. For example, referring to <FIG>, the UE <NUM> may perform the rank-based cell reselection procedure by determining (at <NUM>) that a first signal strength associated with the serving base station meets a reselection threshold criteria. For the rank-based reselection procedure, an IDLE mode UE <NUM> may enter a wake mode of every DRX cycle to measure the signal of the serving base station <NUM> (Qmeas,s) and determine (at <NUM>) the received signal level (Srxlev) of the serving base station <NUM> to determine whether to remain camped on the serving cell (e.g., the serving base station <NUM>) or to reselect to a neighbor cell. Here, the transmission and reception conditions the UE <NUM> may be reflected in the determination (at <NUM>), for example, by applying minimum received signal level (Qrxlevmin), allowed maximum TX power level PEMAX, etc. If the received signal level (Srxlev) of the serving base station <NUM> is greater than or equal to the specified threshold value (s-IntraSearch), the UE <NUM> may remain camped on the serving cell. Otherwise, the UE <NUM> determines (at <NUM>) that the signal strength of the serving base station <NUM> is less than the specified threshold value (s-IntraSearch).

At <NUM>, the UE may perform the rank-based cell reselection procedure by determining a respective second signal strength associated with each of a second set of neighbor base stations upon determining that the first signal strength meets the reselection threshold criteria. In certain aspects, the second set of neighbor base stations may be different than the first set of neighbor base stations. For example, referring to <FIG>, the UE <NUM> may perform the rank-based reselection procedure by determining (at <NUM>) a respective second signal strength (Qmeas,n) associated with each of a second set of neighbor base stations <NUM>, <NUM> upon determining (at <NUM>) that the first signal strength meets the reselection threshold criteria. In certain aspects, the second set of neighbor base stations <NUM>, <NUM> may be different than the first set of neighbor base stations <NUM>.

At <NUM>, the UE may perform the rank-based cell reselection procedure by ranking each neighbor base station in the second set of neighbor base stations based on the respective second signal strength for each neighbor base station. For example, referring to <FIG>, the UE <NUM> may perform the rank-based reselection procedure by ranking (at <NUM>) each neighbor base station <NUM>, <NUM> in the second set of neighbor base stations based on the respective second signal strength for each neighbor base station. For example, the UE <NUM> may rank each cell (Rs, Rn) based on the measured signal strength of the serving cell (Qmeas,s) and neighbor cells (Qmeas,n). Parameters used for cell ranking may be communicated to the UE <NUM> through, e.g., SIBs <NUM> and <NUM> from the serving base station <NUM>. The serving base station <NUM> may be ranked using the hysteresis (q-Hyst) value included in SIB <NUM> while the neighbor base stations <NUM>, <NUM> may be ranked based on the offset (q-OffsetCell) value specified for each cell in SIB <NUM>. Once the serving base station <NUM> and each neighbor base station in the second set of neighbor base stations <NUM>, <NUM> are ranked (at <NUM>), the UE <NUM> may determine if the cell reselection criterion is satisfied (Rn > Rs).

At <NUM>, the UE may perform the rank-based cell reselection procedure by reselecting to a highest ranked neighbor base station in the second set of neighbor base stations. For example, referring to <FIG>, upon determining that one or more neighbor base stations <NUM>, <NUM> satisfy the cell reselection criterion, the UE <NUM> may perform the rank-based reselection procedure by reselecting (at <NUM>) to a highest ranked neighbor base station in the second set of neighbor base stations. In certain aspects the highest ranked neighbor base station <NUM> may be operating on, for example, a second RAT that is different than the first RAT. The second RAT may be the second highest priority RAT associated with the UE <NUM>. For example, if the UE <NUM> is associated with <NUM> but either is unsubscribed for <NUM> services or the <NUM> neighbor cell (e.g., first neighbor base station <NUM>) is barred, by using the rank-based reselection mechanism, the UE <NUM> may be able to reselect to the second highest priority RAT instead of having to reselect to the <NUM>rd RAT neighbor base station <NUM> for the reasons discussed above.

At <NUM>, the UE may perform a priority-based cell reselection procedure for the first set of neighbor base stations, instead of the rank-based priority reselection based on signal strength, when the UE is able to reselect to the first RAT. For example, referring to <FIG>, the UE <NUM> may perform (at <NUM>) the priority-based cell reselection procedure for the first set of neighbor base stations when the UE is able to reselect to the first RAT.

At <NUM>, the UE may perform the priority-based cell reselection procedure by reselecting (e.g., as described in connection with <NUM> in <FIG>) to a highest priority base station operating on the preferred radio frequencies that meets a threshold criteria. In one aspect the highest priority base station may be operating on the first of RAT. For example, the UE <NUM> may perform the priority-based cell reselection procedure by reselecting (at <NUM>) to a highest priority base station operating on the preferred radio frequencies that meets a threshold criteria. In one aspect the highest priority base station may be operating on the first of RAT. The reselection priority list may prioritize one or more different neighbor cells operating on the highest priority RAT in the area. Hence, when the UE <NUM> includes a <NUM> SIM card is camped on a <NUM> serving base station <NUM>, the reselection priority list may include a prioritized list of <NUM> neighbor base station(s) <NUM> but not <NUM> neighbor base stations <NUM>. The <NUM> neighbor cells may be prioritized based on system overhead, data rate, etc. The threshold criteria associated with the neighbor base stations prioritized in the reselection priority list may be a minimum signal strength.

Thus, using the mechanism described above in connection with <FIG>, a UE of the present disclosure may perform a rank-based reselection procedure based on signal strength when the UE is unable to reselect to the RAT indicated in the reselection priority list and is camped on a lower priority RAT (e.g., <NUM>rd RAT), thereby reselecting to a second highest priority RAT (e.g., <NUM>nd RAT) associated with the UE, rather than a third highest priority RAT (e.g., <NUM>rd RAT) neighbor cell. For example, when the highest priority RAT is <NUM> (e.g., <NUM>st RAT), the second highest priority RAT may be <NUM> (e.g., <NUM>nd RAT), and the third highest priority RAT may be <NUM> (e.g., <NUM>rd RAT). In another example, when the highest priority RAT is <NUM> (e.g., <NUM>st RAT), the second highest priority RAT may be <NUM> (e.g., <NUM>nd RAT), and the third highest priority RAT may be <NUM> (e.g., <NUM>rd RAT).

<FIG> is a conceptual data flow diagram <NUM> illustrating the data flow between different means/components in an exemplary apparatus <NUM>. The apparatus may be a UE (e.g., the UE <NUM>, <NUM>, <NUM>, the apparatus <NUM>') in communication with a serving base station <NUM> (e.g., the base station <NUM>, <NUM>, <NUM>, the serving base station <NUM>), a neighbor base station <NUM> (e.g., the base station <NUM>, <NUM>, <NUM>, the second neighbor base station <NUM>), and/or a second neighbor base station <NUM> (e.g., the base station <NUM>, <NUM>, <NUM>, the first neighbor base station <NUM>).

The apparatus may include a reception component <NUM>, a reselection priority list component <NUM>, a first RAT component <NUM>, a second RAT component <NUM>, a third RAT component <NUM>, a rank-based reselection component <NUM>, a priority-based reselection component <NUM>, and a transmission component <NUM>.

In certain configurations, the first RAT component <NUM> may be configured to maintain information related to any first RAT services the apparatus is subscribed for, and information indicating whether any neighbor cells operating on the first RAT are barred. In certain other configurations, the second RAT component <NUM> may be configured to maintain information related to any second RAT services the apparatus is subscribed for, and information indicating whether any neighbor cells operating on the second RAT are barred. In certain other configurations, the third RAT component <NUM> may be configured to maintain information related to any third RAT services the apparatus is subscribed for, and information indicating whether any neighbor cells operating on the third RAT are barred.

The reception component <NUM> may be configured to receive a priority list associated with preferred radio frequencies from a serving base station. In certain aspects, each radio frequency of the preferred radio frequencies associated with a first set of base station may operate on a first RAT. In certain aspects, the reselection priority list may be received in a SIB from the serving base station. In certain other aspects, the serving base station may be operating on a RAT that has a lower priority than the first RAT. In certain configurations, the reception component <NUM> may be configured to send a signal associated with the SIB(s) and/or reselection priority list to the reselection priority list component <NUM>. The reselection priority list component <NUM> may determine the RAT (e.g., <NUM>st RAT, <NUM>nd RAT, <NUM>rd RAT) with which the prioritized neighbor cells listed in the reselection priority list are associated. The reselection priority list component <NUM> may be configured to send a signal to the first RAT component <NUM> when the neighbor cells in the reselection prioritized list are operating on the first RAT. The first RAT component <NUM> may be configured to determine if the UE is able to reselect to the first RAT. The first RAT component <NUM> may be configured to send a signal to indicate whether the UE is able to reselect to the first RAT to one or more of the reselection priority list component <NUM>, the rank-based reselection component <NUM>, and/or the priority-based reselection component <NUM>.

When the signal indicates that the UE is not able to reselect to the first RAT, the rank-based reselection component <NUM> may be configured to perform a rank-based cell reselection procedure based on signal strength when the UE is unable to reselect to the first RAT. In certain aspects, the rank-based reselection component <NUM> may be configured to perform the rank-based cell reselection procedure by determining that a first signal strength associated with the serving base station meets a reselection threshold criteria. In certain other aspects, the rank-based reselection component <NUM> may be configured to perform the rank-based cell reselection procedure by determining a respective second signal strength associated with each of a second set of neighbor base stations upon determining that the first signal strength meets the reselection threshold criteria. In certain aspects, the second set of neighbor base stations may be different than the first set of neighbor base stations. In certain other aspects, the rank-based reselection component <NUM> may be configured to perform the rank-based cell reselection procedure by ranking each neighbor base station in the second set of neighbor base stations based on the respective second signal strength for each neighbor base station. In certain other aspects, the rank-based reselection component <NUM> may be configured to perform the rank-based cell reselection procedure by reselecting to a highest ranked neighbor base station in the second set of neighbor base stations, the highest ranked neighbor base station operating on a second RAT, e.g., different than the first RAT. The rank-based reselection may be performed in a RAT independent manner so that the UE may select between base stations operating on different RATs. The rank-based reselection component <NUM> may be configured to send a signal to one or more of the second RAT component <NUM>, the reception component <NUM>, the transmission component <NUM>, and/or the reselection priority list component <NUM> indicating the neighbor base station <NUM> (e.g., <NUM>nd RAT) for which reselection was determined. The transmission component <NUM> and/or reception component <NUM> may be configured to perform a cell acquisition procedure with the neighbor base station <NUM> to acquire the first neighbor cell.

When the signal indicates that the UE is able to reselect to the first RAT, the priority-based reselection component <NUM> may be configured to perform a priority-based cell reselection procedure for the first set of neighbor base stations when the UE is able to reselect to the first RAT. In certain aspects, the priority-based reselection component <NUM> may be configured to perform the priority-based cell reselection procedure by reselecting to a highest priority base station operating on the preferred radio frequencies that meets a threshold criteria. In one aspect the highest priority base station operates on the first of RAT. The priority-based reselection component <NUM> may be configured to send a signal to one or more of the first RAT component <NUM>, the reception component <NUM>, the transmission component <NUM>, and/or the reselection priority list component <NUM> indicating neighbor base station <NUM> (e.g., <NUM>st RAT) for which reselection was determined. The transmission component <NUM> and/or reception component <NUM> may be configured to perform a cell acquisition procedure with the neighbor base station <NUM> to acquire the second neighbor cell.

The components may be one or more hardware components specifically configured to carry out the stated processes/algorithm, implemented by a processor configured to perform the stated processes/algorithm, stored within a computer-readable medium, e.g., a non-transitory computer-readable medium, for implementation by a processor, or some combination thereof.

<FIG> is a diagram <NUM> illustrating an example of a hardware implementation for an apparatus <NUM>' employing a processing system <NUM>. The processing system <NUM> may be implemented with a bus architecture, represented generally by the bus <NUM>. The bus <NUM> may include any number of interconnecting buses and bridges depending on the specific application of the processing system <NUM> and the overall design constraints. The bus <NUM> links together various circuits including one or more processors and/or hardware components, represented by the processor <NUM>, the components <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and the computer-readable medium / memory <NUM>. The bus <NUM> may also link various other circuits such as timing sources, peripherals, voltage regulators, and power management circuits, which are well known in the art, and therefore, will not be described any further.

The processing system <NUM> may be coupled to a transceiver <NUM>. The transceiver <NUM> is coupled to one or more antennas <NUM>. The transceiver <NUM> provides a means for communicating with various other apparatus over a transmission medium. The transceiver <NUM> receives a signal from the one or more antennas <NUM>, extracts information from the received signal, and provides the extracted information to the processing system <NUM>, specifically the reception component <NUM>. In addition, the transceiver <NUM> receives information from the processing system <NUM>, specifically the transmission component <NUM>, and based on the received information, generates a signal to be applied to the one or more antennas <NUM>. The processing system <NUM> includes a processor <NUM> coupled to a computer-readable medium / memory <NUM>. The processor <NUM> is responsible for general processing, including the execution of software stored on the computer-readable medium / memory <NUM>. The software, when executed by the processor <NUM>, instructs the processing system <NUM> to perform the various functions described supra for any particular apparatus, e.g., based on aspects described in connection with the flowcharts in <FIG>, <FIG>, and/or <NUM>. The computer-readable medium / memory <NUM> may also be used for storing data that is manipulated by the processor <NUM> when executing software. The processing system <NUM> further includes at least one of the components <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>. The components may be software components running in the processor <NUM>, resident/stored in the computer readable medium / memory <NUM>, one or more hardware components coupled to the processor <NUM>, or some combination thereof. The processing system <NUM> may be a component of the UE <NUM> and may include the memory <NUM> and/or at least one of the TX processor <NUM>, the RX processor <NUM>, and the controller/processor <NUM>.

In certain configurations, the apparatus <NUM>/<NUM>' for wireless communication may include means for receive a priority list associated with preferred radio frequencies from a serving base station (e.g., at least reception component, processor <NUM>, and or memory <NUM>). In certain aspects, each radio frequency of the preferred radio frequencies associated with a first set of base station may operate on a first RAT. In certain other aspects, the reselection priority list may be received in a SIB from the serving base station. In certain other aspects, the serving base station may be operating on a RAT that has a lower priority than the first RAT. In certain other configurations, the apparatus <NUM>/<NUM>' for wireless communication may include means for determining if the UE is able to reselect to the first RAT (e.g., at least first RAT component <NUM>, processor <NUM>, and or memory <NUM>). In certain other configurations, the apparatus <NUM>/<NUM>' for wireless communication may include means for perform a rank-based cell reselection procedure based on signal strength when the UE is unable to reselect to the first RAT (e.g., at least reselection component <NUM>, processor <NUM>, and or memory <NUM>). In certain aspects, the means for performing the rank-based cell reselection procedure may be configured to determine that a first signal strength associated with the serving base station meets a reselection threshold criteria. In certain other aspects, the means for performing the rank-based cell reselection procedure may be configured to determine a respective second signal strength associated with each of a second set of neighbor base stations upon determining that the first signal strength meets the reselection threshold criteria. In certain aspects, the second set of neighbor base stations may be different than the first set of neighbor base stations. In certain other aspects, the means for performing the rank-based cell reselection procedure may be configured to rank each neighbor base station in the second set of neighbor base stations based on the respective second signal strength for each neighbor base station. In certain other aspects, the means for performing the rank-based cell reselection procedure may be configured to reselect to a highest ranked neighbor base station in the second set of neighbor base stations, the highest ranked neighbor base station operating on a second RAT different from the first RAT. In certain other configurations, the apparatus <NUM>/<NUM>' for wireless communication may include means for performing a priority-based cell reselection procedure for the first set of neighbor base stations when the UE is able to reselect to the first RAT. In certain aspects, the means for performing the priority-based cell reselection procedure may be configured to reselect to a highest priority base station operating on the preferred radio frequencies that meets a threshold criteria. In one aspect the highest priority base station may be operating on the first of RAT. The aforementioned means may be one or more of the aforementioned components of the apparatus <NUM> and/or the processing system <NUM> of the apparatus <NUM>' configured to perform the functions recited by the afore mentioned means.

Claim 1:
A method (<NUM>) of wireless communication of a user equipment, UE (<NUM>, <NUM>, <NUM>), comprising:
receiving (<NUM>, <NUM>) a priority list (<NUM>) associated with preferred radio frequencies from a serving base station (<NUM>, <NUM>, <NUM>), each radio frequency of the preferred radio frequencies associated with a first set of neighbor base stations operating on a first radio access technology, RAT (<NUM>);
determining (<NUM>, <NUM>) if the UE (<NUM>, <NUM>, <NUM>) is able to reselect to the first RAT (<NUM>);
performing (<NUM>, <NUM>) a priority-based cell reselection procedure for the first set of neighbor base stations (<NUM>) when the UE (<NUM>, <NUM>, <NUM>) is able to reselect to the first RAT (<NUM>), based on the priority list (<NUM>); and
performing (<NUM>, <NUM>) a rank-based cell reselection procedure for a second set of neighbor base stations (<NUM>, <NUM>) based on signal strength when the UE (<NUM>, <NUM>, <NUM>) is unable to reselect to the first RAT (<NUM>), wherein the performing the rank-based cell reselection procedure comprises:
determining that a first signal strength associated with the serving base station meets a reselection threshold criteria;
determining a respective second signal strength associated with each of the second set of neighbor base stations upon determining that the first signal strength meets the reselection threshold criteria, the second set of neighbor base stations being different from the first set of neighbor base stations operating on the first RAT;
ranking each neighbor base station in the second set of neighbor base stations based on the respective second signal strength for each neighbor base station; and
reselecting to a highest ranked neighbor base station in the second set of neighbor base stations, the highest ranked neighbor base station operating on a second RAT different from the first RAT.