WO2021232374A1

WO2021232374A1 - Empirical data based 5g network search for performing 5g network reselection from a legacy network

Info

Publication number: WO2021232374A1
Application number: PCT/CN2020/091642
Authority: WO
Inventors: Hao Zhang; Jian Li; Chaofeng HUI; Fojian ZHANG; Yuankun ZHU; Yi Liu; Tianya LIN; Miao Fu; Hong Wei
Original assignee: Qualcomm Incorporated
Priority date: 2020-05-21
Filing date: 2020-05-21
Publication date: 2021-11-25

Abstract

This disclosure provides systems, methods, and apparatus, including computer programs encoded on computer-readable media, for selecting a periodic search time interval associated with a 5G cell search. In some aspects, a user equipment (UE) that is registered with a legacy cell associated with a wireless wide area network (WWAN) legacy radio access technology (RAT) may determine whether the UE previously found a 5G cell while registered with the legacy cell. The UE may determine whether the UE previously found a 5G cell while registered with the legacy cell based on whether the legacy cell is listed in a 5G cell available list or a 5G cell not available list. The UE may select a periodic search time interval for the 5G cell search process based on whether the legacy cell is listed in a 5G cell available list or a 5G cell not available list.

Description

EMPIRICAL DATA BASED 5G NETWORK SEARCH FOR PERFORMING 5G NETWORK RESELECTION FROM A LEGACY NETWORK

TECHNICAL FIELD

Aspects of the present disclosure relate generally to wireless communication and to techniques for selection of a periodic search time interval associated with a 5G network search for performing a 5G network reselection from a legacy network.

DESCRIPTION OF THE RELATED TECHNOLOGY

Wireless communications systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems may be capable of supporting communication with multiple users by sharing the available system resources (such as time, frequency, and power) . A wireless multiple-access communications system may include a number of base stations (BSs) , each simultaneously supporting communications for multiple communication devices, which may be otherwise known as user equipment (UE) .

To meet the growing demands for expanded mobile broadband connectivity, wireless communication technologies are advancing from the 3 ^rd generation (3G) and long term evolution (LTE) technologies to a next generation new radio (NR) technology, which may be referred to as 5 ^th Generation (5G) or 5G NR. For example, NR is designed to provide a lower latency, a higher bandwidth or a higher throughput, and a higher reliability than 3G or LTE. NR is designed to operate over a wide array of spectrum bands, for example, from low-frequency bands below about 1 gigahertz (GHz) and mid-frequency bands from about 1 GHz to about 6 GHz, to high-frequency bands such as millimeter wave (mmWave (mmW) ) bands. NR is also designed to operate across different spectrum types, from licensed spectrum to unlicensed and shared spectrum. Spectrum sharing enables operators to opportunistically aggregate spectrums to dynamically support high-bandwidth services. Spectrum sharing can extend the benefit of NR technologies to operating entities that may not have access to a licensed spectrum.

Wireless communication networks may support some combination of 2G, 3G, LTE, and 5G NR technologies. A UE may communicate with the wireless communication network using one or more of the 2G, 3G, LTE, and 5G NR technologies. For example, the UE may use 5G NR for some applications, such as data transmissions, and may use LTE for other applications, such as voice transmissions. A UE also may have access to wireless local area networks (WLANs) in the wireless communication network.

SUMMARY

The systems, methods, and devices of this disclosure each have several innovative aspects, no single one of which is solely responsible for the desirable attributes disclosed herein.

One innovative aspect of the subject matter described in this disclosure can be implemented in a method for wireless communication performed by an apparatus of a user equipment (UE) . The method may include determining, while the UE is registered with a legacy cell associated with a wireless wide area network (WWAN) legacy radio access technology (RAT) , to perform a 5G cell search process to search for a 5G New Radio (NR) RAT. The method may include determining whether the UE previously found a 5G cell associated with the 5G NR RAT while registered with the legacy cell associated with the WWAN legacy RAT. The method may include determining a periodic search time interval for the 5G cell search process based on whether the UE previously found a 5G cell associated with the 5G NR RAT while registered with the legacy cell, and performing the 5G cell search process based on the periodic search time interval to search for a 5G cell associated with the 5G NR RAT.

In some implementations, the method of determining whether the UE previously found a 5G cell associated with the 5G NR RAT while registered with the legacy cell may include determining whether a first cell list maintained by the UE includes the legacy cell, and determining that the UE previously found a 5G cell associated with the 5G NR RAT while registered with the legacy cell in response to determining that the first cell list includes the legacy cell.

In some implementations, the method may include determining whether a second cell list maintained by the UE includes the legacy cell in response to determining that the first cell list does not includes the legacy cell, and determining that the UE has not previously found a 5G cell associated with the 5G NR RAT while registered with the legacy cell in response to determining that the second cell list includes the legacy cell.

In some implementations, the method of determining the periodic search time interval for the 5G cell search process based on whether the UE previously found a 5G cell associated with the 5G NR RAT while registered with the legacy cell may include selecting a first periodic search time interval for the 5G cell search process in response to determining that the first cell list includes the legacy cell, and selecting a second periodic search time interval for the 5G cell search process in response to determining that the second cell list includes the legacy cell. The first periodic search time interval may be a shorter time interval than the second periodic search time interval.

In some implementations, the method of performing the 5G cell search process based on the periodic search time interval may include performing the 5G cell search process based on the first periodic search time interval in response to determining that the first cell list includes the legacy cell, or performing the 5G cell search process based on the second periodic search time interval in response to determining that the second cell list includes the legacy cell.

In some implementations, the first cell list may be a 5G cell available list maintained by the UE, and the second cell list may be a 5G cell not available list maintained by the UE.

In some implementations, the method may include determining that the UE has not previously searched for a 5G cell associated with the 5G NR RAT while registered with the legacy cell in response to determining that the first cell list and second cell list do not includes the legacy cell, and selecting a third periodic search time interval for the 5G cell search process in response to determining that the first cell list and second cell list do not include the legacy cell. The first periodic search time interval may be a shorter time interval than the third periodic search time interval, and the third periodic search time interval may be a shorter time interval than the second periodic search time interval.

In some implementations, the method may include performing the 5G cell search process based on the third periodic search time interval in response to determining that the UE has not previously searched for a 5G cell associated with the 5G NR RAT while registered with the legacy cell, adding the legacy cell to the first cell list in response to finding a 5G cell associated with the 5G NR RAT using the 5G cell search process, and adding the legacy cell to the second cell list in response to not finding a 5G cell associated with the 5G NR RAT using the 5G cell search process.

In some implementations, the WWAN legacy RAT includes a 2G RAT or a 3G RAT.

In some implementations, the method of performing the 5G cell search process based on the periodic search time interval may include performing the 5G cell search process after expiration of the periodic search time interval.

In some implementations, the 5G cell search process may be a background 5G cell search process performed by the UE during an idle mode.

In some implementations, the method may include performing a reselection from the WWAN legacy RAT to the 5G NR RAT in response to searching and finding a 5G cell associated with the 5G NR RAT.

In some implementations, the method of determining the periodic search time interval for the 5G cell search process based on whether the UE previously found a 5G cell associated with the 5G NR RAT while registered with the legacy cell may include selecting a first periodic search time interval for the 5G cell search process in response to determining that the UE previously found a 5G cell associated with the 5G NR RAT while registered with the legacy cell, and selecting a second periodic search time interval for the 5G cell search process in response to determining that the UE has not previously found a 5G cell associated with the 5G NR RAT while registered with the legacy cell. The first periodic search time interval may be a shorter time interval than the second periodic search time interval.

In some implementations, the method may include determining that the UE has not previously searched for a 5G cell associated with the 5G NR RAT while registered with the legacy cell, and selecting a third periodic search time interval for the 5G cell search process in response to determining that the UE has not previously searched for a 5G cell associated with the 5G NR RAT while registered with the legacy cell. The first periodic search time interval may be a shorter time interval than the third periodic search time interval, and the third periodic search time interval may be a shorter time interval than the second periodic search time interval.

Another innovative aspect of the subject matter described in this disclosure can be implemented in an apparatus that includes one or more processors and one or more interfaces. The one or more processors and the one or more interfaces may be configured to perform any of the above-mentioned methods.

Another innovative aspect of the subject matter described in this disclosure can be implemented in a wireless communication device, such as a BS or a UE, which includes the above-mentioned apparatus that is configured to perform any of the above-mentioned methods.

Aspects of the subject matter described in this disclosure can be implemented in a device, a software program, a system, or other means to perform any of the above-mentioned methods.

Details of one or more implementations of the subject matter described in this disclosure are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages will become apparent from the description, the drawings and the claims. Note that the relative dimensions of the following figures may not be drawn to scale.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a system diagram of an example wireless communication network.

Figure 2 is a block diagram conceptually illustrating an example of a base station (BS) in communication with a user equipment (UE) .

Figure 3 shows a system diagram of an example wireless communication network including a UE that is configured to select a periodic search time interval associated with a 5G cell search process for performing a 5G network reselection from a legacy network..

Figure 4 depicts a flowchart with example operations performed by an apparatus of a UE for selecting a periodic search time interval associated with a 5G cell search process for performing a 5G network reselection from a legacy network.

Figure 5 depicts a flowchart with example operations performed by an apparatus of a UE for assigning a legacy cell to a cell list associated with a 5G cell search process.

Figure 6 shows a block diagram of an example wireless communication apparatus.

Figure 7 shows a block diagram of an example mobile communication device.

Like reference numbers and designations in the various drawings indicate like elements.

DETAILED DESCRIPTION

The following description is directed to certain implementations for the purposes of describing the innovative aspects of this disclosure. However, a person having ordinary skill in the art will readily recognize that the teachings herein can be applied in a multitude of different ways. The examples in this disclosure are based on wireless network communications in wide area networks (WANs) . However, the described implementations may be implemented in any device, system or network that is capable of transmitting and receiving radio frequency signals according to any of the wireless communication standards, including any of the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standards, the

standard, code division multiple access (CDMA) , time division multiple access (TDMA) , frequency division multiple access (FDMA) , orthogonal FDMA (OFDMA) , single-carrier FDMA (SC-FDMA) , Global System for Mobile communications (GSM) , GSM/General Packet Radio Service (GPRS) , Enhanced Data GSM Environment (EDGE) , Terrestrial Trunked Radio (TETRA) , Wideband-CDMA (W-CDMA) , Evolution Data Optimized (EV-DO) , 1xEV-DO, EV-DO Rev A, EV-DO Rev B, High Speed Packet Access (HSPA) , High Speed Downlink Packet Access (HSDPA) , High Speed Uplink Packet Access (HSUPA) , Evolved High Speed Packet Access (HSPA+) , Long Term Evolution (LTE) , 5 ^th Generation (5G) or new radio (NR) , Advanced Mobile Phone Service (AMPS) , or other known signals that are used to communicate within a wireless, cellular or internet of things (IoT) network, such as a system utilizing 3G, 4G or 5G, or further implementations thereof, technology.

A wireless communication network (which also may be referred to as a wireless WAN or WWAN) may include a 5G NR radio access technology (RAT) of a 5G NR network and an LTE RAT of an LTE network. The wireless communication network also may include a legacy RAT of a legacy network, such as a 3G RAT of a 3G network or a 2G RAT of a 2G network. The RATs of a WWAN also may be referred to as WWAN RATs. A user equipment (UE) of the wireless communication network may use the 5G NR RAT, the LTE RAT, or a legacy RAT depending on which wireless coverage is available to the UE and which wireless coverage provides the best quality service.

When a UE is registered with a legacy RAT (such as a 2G RAT or a 3G RAT) , the UE may perform a background 5G cell search process to register with a 5G NR RAT. The UE may perform the background 5G cell search process when the UE is in an idle mode. For example, the UE may perform the background 5G cell search process during a discontinuous reception (DRX) gap when the UE is in an idle mode.

In some implementations, after the UE determines to perform a reselection from a legacy cell associated with the legacy RAT to a 5G cell associated with the 5G NR RAT, the UE may determine whether the UE has previously found a 5G cell associated with a 5G NR RAT while registered with the legacy cell. The UE may determine a periodic search time interval for the 5G cell search process based on whether the UE previously found a 5G cell associated with the 5G NR RAT while registered with the legacy cell. In some implementations, the UE may determine whether the legacy cell is included in a 5G cell available list maintained by the UE in order to determine whether the UE previously found a 5G cell while registered with the legacy cell. If the 5G cell available list includes the legacy cell, then the UE previously found a 5G cell while registered with the legacy cell. If the 5G cell available list does not include the legacy cell, the UE may determine whether the legacy cell is included in a 5G cell not available list maintained by the UE. If the 5G cell not available list includes the legacy cell, the UE may determine that the UE has not previously found a 5G cell while registered with the legacy cell. Furthermore, if the legacy cell is not listed in either the 5G cell available list or the 5G cell not available list, the UE may not have previously searched for a 5G cell while registered with the legacy cell.

In some implementations, the UE may select a first periodic search time interval for the 5G cell search process if the UE determines that the 5G cell available list includes the legacy cell. The UE may select a second periodic search time interval for the 5G cell search process if the UE determines the 5G cell not available list includes the legacy cell. The UE may select a third periodic search time interval for the 5G cell search process if the UE determines that the legacy cell is not listed in either the 5G cell available list or the 5G cell not available list. In some implementations, the first periodic search time interval may be a shorter time interval than both the second periodic search time interval and the third periodic search time interval. Also, the third periodic search time interval may be a shorter time interval than the second periodic search time interval. In some implementations, the first periodic search time interval may be referred to as a short periodic search time interval, or T_short. The second periodic search time interval may be referred to as a long periodic search time interval, or T_long. The third periodic search time interval may be referred to as a normal periodic search time interval, or T_normal. In some implementations, the UE may perform the 5G cell search process based on the selected periodic search time interval to search for a 5G cell associated with the 5G NR RAT. After searching for and finding a 5G cell using the 5G cell search process, the UE may register with the 5G cell.

Particular implementations of the subject matter described in this disclosure can be implemented to realize one or more of the following potential advantages. The UE determining the periodic search time interval to use for a 5G cell search process based on whether the UE has previously found a 5G cell while registered with the legacy cell may allow the UE to switch from the legacy cell to a 5G cell within a shorter amount of time. Selecting the shortest periodic search time interval when the UE has previously found a 5G cell while registered with the legacy cell may increase the frequency when the UE performs the 5G cell search process. Increasing the frequency when the 5G cell search process is triggered may result in the UE finding a 5G cell in a shorter amount of time compared to when a default (or normal) periodic search time interval is used. Finding and registering with a 5G cell in a shorter amount of time also may improve the user experience since the UE may begin to receive 5G services. Furthermore, selecting the longest periodic search time interval when the UE has not previously found a 5G cell while registered with the legacy cell may decrease the frequency when the UE performs the 5G cell search process, and thus may save power compared to when a default (or normal) periodic search time interval is used.

Figure 1 is a system diagram of an example wireless communication network 100. The wireless communication network 100 may be an LTE network or a 5G NR network, or a combination thereof. The wireless communication network 100 also may be referred to as a wide area network (WAN) or a wireless wide area network (WWAN) . The wireless communication network 100 includes a number of base stations (BSs) 105 (individually labeled as 105A, 105B, 105C, 105D, 105E, and 105F) and other network entities. A BS 105 may be a station that communicates with UEs 115 and also may be referred to as an evolved node B (eNB) , a next generation eNB (gNB) , an access point, and the like. In some implementations, a BS 105 may represent an eNB of an LTE network or a gNB of a 5G NR network, or a combination thereof. Each BS 105 may provide communication coverage for a particular geographic area. In 3GPP, the term “cell” can refer to this particular geographic coverage area of a BS 105 or a BS subsystem serving the coverage area, depending on the context in which the term is used.

A BS 105 may provide communication coverage for a macro cell or a small cell, such as a pico cell or a femto cell, or other types of cells. A macro cell generally covers a relatively large geographic area (such as several kilometers in radius) and may allow unrestricted access by UEs with service subscriptions with the network provider. A pico cell generally covers a relatively smaller geographic area and may allow unrestricted access by UEs with service subscriptions with the network provider. A femto cell generally covers a relatively small geographic area (such as a home) and, in addition to unrestricted access, also may provide restricted access by UEs having an association with the femto cell (such as UEs in a closed subscriber group (CSG) , UEs for users in the home, and the like) . A BS for a macro cell may be referred to as a macro BS. A BS for a small cell may be referred to as a small cell BS, a pico BS, a femto BS or a home BS. In the example shown in Figure 1, the

BSs

105D and 105E may be regular macro BSs, while the BSs 105A-105C may be macro BSs enabled with three dimensions (3D) , full dimensions (FD) , or massive MIMO. The BSs 105A-105C may take advantage of their higher dimension MIMO capabilities to exploit 3D beamforming in both elevation and azimuth beamforming to increase coverage and capacity. The BS 105F may be a small cell BS which may be a home node or portable access point. A BS 105 may support one or multiple (such as two, three, four, and the like) cells.

The wireless communication network 100 may support synchronous or asynchronous operation. For synchronous operation, the BSs may have similar frame timing, and transmissions from different BSs may be approximately aligned in time. For asynchronous operation, the BSs may have different frame timing, and transmissions from different BSs may not be aligned in time.

The UEs 115 are dispersed throughout the wireless communication network 100, and each UE 115 may be stationary or mobile. A UE 115 also may be referred to as a terminal, a mobile station, a wireless device, a subscriber unit, a station, or the like. A UE 115 may be a mobile phone, a personal digital assistant (PDA) , a wireless modem, a wireless communication device, a handheld device, a wearable device, a tablet computer, a laptop computer, a cordless phone, a wireless local loop (WLL) station, a smart appliance, a drone, a video camera, a sensor, or the like. In one aspect, a UE 115 may be a device that includes a Universal Integrated Circuit Card (UICC) . In another aspect, a UE may be a device that does not include a UICC. In some aspects, the UEs 115 that do not include UICCs also may be referred to as IoT devices or internet of everything (IoE) devices. The UEs 115A-115D are examples of mobile smart phone-type devices that may access the wireless communication network 100. A UE 115 also may be a machine specifically configured for connected communication, including machine type communication (MTC) , enhanced MTC (eMTC) , narrowband IoT (NB-IoT) , and the like. The UEs 115E-115L are examples of various machines configured for communication that access the wireless communication network 100. A UE 115 may be able to communicate with any type of the BSs, whether macro BS, small cell, or the like. In Figure 1, a lightning bolt is representative of a communication link that indicates wireless transmissions between a UE 115 and a serving BS 105, which is a BS designated to serve the UE 115 on the downlink and uplink, or desired transmission between BSs, and backhaul transmissions between BSs.

In operation, the BSs 105A-105C may serve the

UEs

115A and 115B using 3D beamforming and coordinated spatial techniques, such as coordinated multipoint (CoMP) or multi-connectivity. The macro BS 105D may perform backhaul communications with the BSs 105A-105C, as well as the BS 105F (which may be a small cell BS) . The macro BS 105D also may transmit multicast services which are subscribed to and received by the UEs 115C and 115D. Such multicast services may include mobile television or stream video, or may include other services for providing community information, such as weather emergencies or alerts, such as Amber alerts or gray alerts.

The BSs 105 also may communicate with a core network. The core network may provide user authentication, access authorization, tracking, Internet Protocol (IP) connectivity, and other access, routing, or mobility functions. At least some of the BSs 105 (such as a gNB or an access node controller (ANC) ) may interface with the core network through backhaul links (such as NG-C and NG-U) and may perform radio configuration and scheduling for communication with the UEs 115. In various examples, the BSs 105 may communicate, either directly or indirectly (such as through core network) , with each other over backhaul links, which may be wired or wireless communication links.

The wireless communication network 100 also may support mission critical communications with ultra-reliable and redundant links for mission critical devices, such as the UE 115E, which may be a drone. Redundant communication links with the UE 115E may include links from the

macro BSs

105D and 105E, as well as links from the small cell BS 105F. Other machine type devices, such as the UE 115F and UE 115G (such as video cameras or smart lighting) , the UE 115H (such as a smart meter) , and UE 115I (such as a wearable device) may communicate through the wireless communication network 100 either directly with the BSs, such as the small cell BS 105F, and the macro BS 105E, or in multi-hop configurations by communicating with another user device which relays its information to the wireless communication network 100. For example, the UE 115H may communicate smart meter information to the UE 115I (such as a wearable device or mobile phone) , which may then report to the wireless communication network 100 through the small cell BS 105F. The wireless communication network 100 also may provide additional network efficiency through dynamic, low-latency TDD/FDD communications, such as in vehicle-to-vehicle (V2V) communications, as shown by UEs 115J-115L. Furthermore, the wireless communication network 100 may include one or more access points (APs) 107 that are part of one or more wireless local area networks (WLANs) . The APs 107 (which also may be referred to as WLAN APs) may provide short-range wireless connectivity to the UEs 115 of the wireless communication network 100.

In some implementations, the wireless communication network 100 may utilize OFDM-based waveforms for communications. An OFDM-based system may partition the system BW into multiple (K) orthogonal subcarriers, which are also commonly referred to as subcarriers, tones, bins, or the like. Each subcarrier may be modulated with data. In some instances, the subcarrier spacing between adjacent subcarriers may be fixed, and the total number of subcarriers (K) may be dependent on the system BW. The system BW also may be partitioned into subbands. In other instances, the subcarrier spacing and/or the duration of TTIs may be scalable.

The BSs 105 may assign or schedule transmission resources (such as in the form of time-frequency resource blocks (RB) ) for downlink (DL) and uplink (UL) transmissions in the wireless communication network 100. DL refers to the transmission direction from a BS 105 to a UE 115, whereas UL refers to the transmission direction from a UE 115 to a BS 105. The communication can be in the form of radio frames. A radio frame may be divided into a plurality of subframes or slots. Each slot may be further divided into mini-slots. In a FDD mode, simultaneous UL and DL transmissions may occur in different frequency bands. For example, each subframe includes a UL subframe in a UL frequency band and a DL subframe in a DL frequency band. In a TDD mode, UL and DL transmissions occur at different time periods using the same frequency band. For example, a subset of the subframes (such as the DL subframes) in a radio frame may be used for DL transmissions, and another subset of the subframes (such as the UL subframes) in the radio frame may be used for UL transmissions.

The DL subframes and the UL subframes can be further divided into several regions. For example, each DL or UL subframe may have pre-defined regions for transmissions of reference signals, control information, and data. Reference signals are predetermined signals that facilitate the communications between the BSs 105 and the UEs 115. For example, a reference signal can have a particular pilot pattern or structure, where pilot tones may span across an operational BW or frequency band, each positioned at a pre-defined time and a pre-defined frequency. For example, a BS 105 may transmit cell-specific reference signals (CRSs) or channel state information reference signals (CSI-RSs) to enable a UE 115 to estimate a DL channel. Similarly, a UE 115 may transmit sounding reference signals (SRSs) to enable a BS 105 to estimate a UL channel. Control information may include resource assignments and protocol controls. Data may include protocol data and operational data. In some aspects, the BSs 105 and the UEs 115 may communicate using self-contained subframes. A self-contained subframe may include a portion for DL communication and a portion for UL communication. A self-contained subframe can be DL-centric or UL-centric. A DL-centric subframe may include a longer duration for DL communication than for UL communication. A UL-centric subframe may include a longer duration for UL communication than for UL communication.

In some aspects, the wireless communication network 100 may be an NR network deployed over a licensed spectrum or an NR network deployed over an unlicensed spectrum (such as NR-U and NR-U lite networks) . The BSs 105 can transmit synchronization signals, including a primary synchronization signal (PSS) and a secondary synchronization signal (SSS) , in the wireless communication network 100 to facilitate synchronization. The BSs 105 can broadcast system information associated with the wireless communication network 100 (such as a master information block (MIB) , remaining system information (RMSI) , and other system information (OSI) ) to facilitate initial network access. In some instances, the BSs 105 may broadcast one or more of the PSS, the SSS, and the MIB in the form of synchronization signal block (SSBs) over a physical broadcast channel (PBCH) and may broadcast one or more of the RMSI and the OSI over a physical downlink shared channel (PDSCH) .

In some aspects, a UE 115 attempting to access the wireless communication network 100 may perform an initial cell search by detecting a PSS included in an SSB from a BS 105. The PSS may enable synchronization of period timing and may indicate a physical layer identity value. The UE 115 may then receive an SSS included in an SSB from the BS 105. The SSS may enable radio frame synchronization, and may provide a cell identity value, which may be combined with the physical layer identity value to identify the cell. The PSS and the SSS may be located in a central portion of a carrier or any suitable frequencies within the carrier.

After receiving the PSS and SSS, the UE 115 may receive an MIB. The MIB may include system information for initial network access and scheduling information for at least one of an RMSI and OSI. After decoding the MIB, the UE 115 may receive at least one of an RMSI and OSI. The RMSI and OSI may include radio resource control (RRC) information related to random access channel (RACH) procedures, paging, control resource set (CORESET) for physical downlink control channel (PDCCH) monitoring, physical uplink control channel (PUCCH) , physical uplink shared channel (PUSCH) , power control, and SRS.

After obtaining one or more of the MIB, the RMSI and the OSI, the UE 115 can perform a random access procedure to establish a connection with the BS 105. In some examples, the random access procedure may be a four-step random access procedure. For example, the UE 115 may transmit a physical random access channel (PRACH) , such as a PRACH preamble, and the BS 105 may respond with a random access response (RAR) . The RAR may include one or more of a detected random access preamble identifier (ID) corresponding to the PRACH preamble, timing advance (TA) information, a UL grant, a temporary cell-radio network temporary identifier (C-RNTI) , and a backoff indicator. Upon receiving the RAR, the UE 115 may transmit a connection request to the BS 105 and the BS 105 may respond with a connection response. The connection response may indicate a contention resolution. In some examples, the PRACH, the RAR, the connection request, and the connection response can be referred to as message 1 (MSG1) , message 2 (MSG2) , message 3 (MSG3) , and message 4 (MSG4) , respectively. In some examples, the random access procedure may be a two-step random access procedure, where the UE 115 may transmit a PRACH (including a PRACH preamble) and a connection request in a single transmission and the BS 105 may respond by transmitting a RAR and a connection response in a single transmission.

After establishing a connection, the UE 115 and the BS 105 can enter a normal operation stage, where operational data may be exchanged. For example, the BS 105 may schedule the UE 115 for UL and DL communications. The BS 105 may transmit UL and DL scheduling grants to the UE 115 via a PDCCH. The BS 105 may transmit a DL communication signal to the UE 115 via a PDSCH according to a DL scheduling grant. The UE 115 may transmit a UL communication signal to the BS 105 via a PUSCH or PUCCH according to a UL scheduling grant.

In some aspects, the wireless communication network 100 may operate over a system BW or a component carrier BW. The wireless communication network 100 may partition the system BW into multiple bandwidth parts (BWPs) . A BWP may be a certain portion of the system BW. For example, if the system BW is 100 MHz, the BWPs may each be 20 MHz or less. A BS 105 may dynamically assign a UE 115 to operate over a certain BWP. The assigned BWP may be referred to as the active BWP. The UE 115 may monitor the active BWP for signaling information from the BS 105. The BS 105 may schedule the UE 115 for UL or DL communications in the active BWP. In some implementations, the BS 105 may configure UEs 115 with narrowband operation capabilities (such as with transmission and reception limited to a BW of 20 MHz or less) to perform BWP hopping for channel monitoring and communications.

In some aspects, a BS 105 may assign a pair of BWPs within the component carrier to a UE 115 for UL and DL communications. For example, the BWP pair may include one BWP for UL communications and one BWP for DL communications. The BS 105 may additionally configure the UE 115 with one or more CORESETs in a BWP. A CORESET may include a set of frequency resources spanning a number of symbols in time. The BS 105 may configure the UE 115 with one or more search spaces for PDCCH monitoring based on the CORESETS. The UE 115 may perform blind decoding in the search spaces to search for DL control information (such as UL or DL scheduling grants) from the BS 105. For example, the BS 105 may configure the UE 115 with one or more of the BWPs, the CORESETS, and the PDCCH search spaces via RRC configurations.

In some aspects, the wireless communication network 100 may operate over a shared frequency band or an unlicensed frequency band, for example, at about 3.5 gigahertz (GHz) , sub-6 GHz or higher frequencies in the mmWave band. The wireless communication network 100 may partition a frequency band into multiple channels, for example, each occupying about 20 MHz. The BSs 105 and the UEs 115 may be operated by multiple network operating entities sharing resources in the shared communication medium and may employ a LBT procedure to acquire channel occupancy time (COT) in the share medium for communications. A COT may be non-continuous in time and may refer to an amount of time a wireless node can send frames when it has won contention for the wireless medium. Each COT may include a plurality of transmission slots. A COT also may be referred to as a transmission opportunity (TXOP) . The BS 105 or the UE 115 may perform an LBT in the frequency band prior to transmitting in the frequency band. The LBT can be based on energy detection or signal detection. For energy detection, the BS 105 or the UE 115 may determine that the channel is busy or occupied when a signal energy measured from the channel is greater than a certain signal energy threshold. For signal detection, the BS 105 or the UE 115 may determine that the channel is busy or occupied when a certain reservation signal (such as a preamble signal sequence) is detected in the channel.

Figure 2 is a block diagram conceptually illustrating an example 200 of a BS 110 in communication with a UE 120. In some aspects, BS 110 and UE 120 may respectively be one of the BSs and one of the UEs in wireless communication network 100 of Figure 1. BS 110 may be equipped with T antennas 234A through 234T, and UE 120 may be equipped with R antennas 252A through 252R, where in general T ≥ 1 and R ≥ 1.

At BS 110, a transmit processor 220 may receive data from a data source 212 for one or more UEs, select one or more modulation and coding schemes (MCS) for each UE based at least in part on channel quality indicators (CQIs) received from the UE, process (for example, encode and modulate) the data for each UE based at least in part on the MCS (s) selected for the UE, and provide data symbols for all UEs. The transmit processor 220 also may process system information (for example, for semi-static resource partitioning information (SRPI) , etc. ) and control information (for example, CQI requests, grants, upper layer signaling, etc. ) and provide overhead symbols and control symbols. The transmit processor 220 also may generate reference symbols for reference signals (for example, the cell-specific reference signal (CRS) ) and synchronization signals (for example, the primary synchronization signal (PSS) and secondary synchronization signal (SSS) ) . A transmit (TX) multiple-input multiple-output (MIMO) processor 230 may perform spatial processing (for example, precoding) on the data symbols, the control symbols, the overhead symbols, or the reference symbols, if applicable, and may provide T output symbol streams to T modulators-demodulators (MODs-DEMODs) 232A through 232T (which also may be referred to as mods/demods or modems) . Each MOD-DEMOD 232 may process a respective output symbol stream (for example, for OFDM, etc. ) to obtain an output sample stream. Each MOD-DEMOD 232 may further process (for example, convert to analog, amplify, filter, and upconvert) the output sample stream to obtain a downlink signal. T downlink signals from MODs-DEMODs 232A through 232T may be transmitted via T antennas 234A through 234T, respectively. According to various aspects described in more detail below, the synchronization signals can be generated with location encoding to convey additional information.

At UE 120, antennas 252A through 252R may receive the downlink signals from BS 110 or other BSs and may provide received signals to modulators-demodulators (MODs-DEMODs) 254A through 254R, respectively (which also may be referred to as mods/demods or modems) . Each MOD-DEMOD 254 may condition (for example, filter, amplify, downconvert, and digitize) a received signal to obtain input samples. Each MOD-DEMOD 254 may further process the input samples (for example, for OFDM, etc. ) to obtain received symbols. A MIMO detector 256 may obtain received symbols from all R MODs-DEMODs 254A through 254R, perform MIMO detection on the received symbols if applicable, and provide detected symbols. A receive processor 258 may process (for example, demodulate and decode) the detected symbols, provide decoded data for UE 120 to a data sink 260, and provide decoded control information and system information to a controller or processor (controller/processor) 280. A channel processor may determine reference signal received power (RSRP) , received signal strength indicator (RSSI) , reference signal received quality (RSRQ) , channel quality indicator (CQI) , etc. In some aspects, one or more components of UE 120 may be included in a housing.

On the uplink, at UE 120, a transmit processor 264 may receive and process data from a data source 262 and control information (for example, for reports including RSRP, RSSI, RSRQ, CQI, etc. ) from controller/processor 280. Transmit processor 264 also may generate reference symbols for one or more reference signals. The symbols from transmit processor 264 may be precoded by a TX MIMO processor 266 if applicable, further processed by MODs-DEMODs 254A through 254R (for example, for DFT-s-OFDM, CP-OFDM, etc. ) , and transmitted to BS 110. At BS 110, the uplink signals from UE 120 and other UEs may be received by antennas 234, processed by MOD-DEMOD 232, detected by a MIMO detector 236 if applicable, and further processed by a receive processor 238 to obtain decoded data and control information sent by UE 120. Receive processor 238 may provide the decoded data to a data sink 239 and the decoded control information to a controller or processor (i.e., controller/processor) 240. The BS 110 may include communication unit 244 and may communicate to network controller 130 via communication unit 244. The network controller 130 may include communication unit 294, a controller or processor (i.e., controller/processor) 290, and memory 292.

The controller/processor 240 of BS 110, the controller/processor 280 of UE 120, or any other component (s) of Figure 2 may perform one or more techniques associated with selecting a periodic search time interval associated with a 5G cell search process, as described in more detail elsewhere herein. For example, the controller/processor 240 of BS 110, the controller/processor 280 of UE 120, or any other component (s) (or combinations of components) of Figure 2 may perform or direct operations of, for example, the process depicted by flowchart 400 of Figure 4, the process depicted by flowchart 500 of Figure 5, or other processes as described herein, such as the processes described in Figure 3. The

memories

242 and 282 may store data and program codes for BS 110 and UE 120, respectively. A scheduler 246 may schedule UEs for data transmission on the downlink, the uplink, or a combination thereof.

The stored program codes, when executed by the controller/processor 280 or other processors and modules at UE 120, may cause the UE 120 to perform operations described with respect to the process depicted by flowchart 400 of Figure 4, the process depicted by flowchart 500 of Figure 5, or other processes as described herein, such as the processes described in Figure 3. The stored program codes, when executed by the controller/processor 240 or other processors and modules at BS 110, may cause the BS 110 to perform operations described with respect to the process depicted by flowchart 400 of Figure 4, the process depicted by flowchart 500 of Figure 5, or other processes as described herein, such as the processes described in Figure 3. A scheduler 246 may schedule UEs for data transmission on the downlink, the uplink, or a combination thereof.

In some aspects, UE 120 may include means for performing the process depicted by flowchart 400 of Figure 4, the process depicted by flowchart 500 of Figure 5, or other processes as described herein, such as the processes described in Figure 3. In some aspects, such means may include one or more components of UE 120 described in connection with Figure 2.

In some aspects, BS 110 may include means for performing the process depicted by flowchart 400 of Figure 4, the process depicted by flowchart 500 of Figure 5, or other processes as described herein, such as the processes described in Figure 3. In some aspects, such means may include one or more components of BS 110 described in connection with Figure 2.

While blocks in Figure 2 are illustrated as distinct components, the functions described above with respect to the blocks may be implemented in a single hardware, software, or combination component or in various combinations of components. For example, the functions described with respect to the transmit processor 264, the receive processor 258, the TX MIMO processor 266, or another processor may be performed by or under the control of controller/processor 280.

Figure 3 shows a system diagram of an example wireless communication network including a UE 120 that is configured to select a periodic search time interval associated with a 5G cell search process for performing a 5G network reselection from a legacy network. A wireless communication network 300 shown in Figure 3 is based on the example wireless communication network 100 described in Figure 1. The wireless communication network 300 also may be referred to as a wide area network (WAN) or a wireless wide area network (WWAN) . The wireless communication network 300 may include the UE 120, a BS 310 of a 5G NR network, and a legacy BS 312 of a legacy network. The UE 120 may be an example implementation of the UE 115 shown in Figure 1 and the UE 120 shown in Figure 2. The BS 310 and the legacy BS 312 may each be an example implementation of the BS 105 shown in Figure 1 and the BS 110 shown in Figure 2. Although not shown for simplicity, the wireless communication network 300 may include one or more additional BSs and one or more additional UEs. In some implementations, the BS 310 may be a gNB that may implement a 5G NR RAT described in this disclosure to manage communications of a 5G NR network. In some implementations, the legacy BS 312 may be a legacy BS that implements any RAT other than an LTE RAT or a 5G NR RAT. For example, the legacy BS 312 may implement a 2G RAT associated with a 2G network or may implement a 3G RAT associated with a 3G network.

In some implementations, the UE 120 may include a connection management unit 322 and a cell search unit 324. In some implementations, the connection management unit 322 may perform operations to establish a wireless connection with a BS of the wireless communication network 300, and may manage the wireless connection, such as to determine whether to maintain the wireless connection or whether to handoff the UE 120 to another BS. For example, the connection management unit 322 may work in conjunction with the cell search unit 324 to determine whether to perform a reselection from a first RAT (such as a legacy RAT) to a second RAT (such as a 5G NR RAT) , as described further herein. In some implementations, the cell search unit 324 may perform a cell search in order to perform a reselection from a first RAT (such as a legacy RAT) to a second RAT (such as a 5G NR RAT) . For example, while the UE 120 is registered with a legacy RAT (such as a 2G RAT or a 3G RAT) , the cell search unit 324 may perform a background 5G cell search to search for and discover a 5G NR RAT in order to perform a reselection. For example, while the UE 120 is registered with the legacy BS 312, the cell search unit 324 may perform a background 5G cell search to search for and discover the BS 310 in order to perform a reselection. The cell search unit 324 may determine a periodic search time interval associated with the background 5G cell search based on information in one or more cell lists that indicate whether the UE 120 previously found a 5G cell associated with a 5G NR RAT while registered with a legacy cell associated with a legacy RAT. For example, the cell search unit 324 may determine a periodic search time interval associated with the background 5G cell search based on information in a 5G cell available list 325 (which also may be referred to as a 5G_cell_available_list) and in a 5G cell not available list 326 (which also may be referred to as 5G_cell_n_available_list) , as described further herein.

In some implementations, the BS 310 may include a connection management unit 316. Although not shown for simplicity, the legacy BS 312 also may include a connection management unit. The connection management unit 316 may perform operations to establish a wireless connection with one or more UEs of the wireless communication network 300 (such as the UE 120) , and may manage the wireless connections, such as to determine whether to maintain the wireless connections or whether to handoff one or more of the UEs to another BS. In some implementations, the connection management unit 322 and the cell search unit 324 may be implemented by the UE 120 using one or more of the components shown in Figure 2 for the UE 120, such as the controller/processor 280 and the memory 282. In some implementations, the connection management unit 316 may be implemented by the BS 310 and the legacy BS 312 shown in Figure 3 using one or more of the components shown in Figure 2 for the BS 110, such as the controller/processor 240, the communication unit 244, and the memory 242.

In some implementations, the UE 120 may determine to perform a reselection from a legacy RAT (such as a 2G RAT or a 3G RAT) to a 5G NR RAT in order to obtain 5G service. For example, the UE 120 may initially establish a wireless connection with a legacy RAT. While the UE 120 is registered with the legacy RAT, the UE 120 may periodically attempt to perform a reselection from the legacy RAT to a 5G NR RAT in order to obtain 5G service. As another example, the UE 120 may initially establish a wireless connection with a 5G NR RAT. However, due to a coverage hole in the coverage area of the 5G network, the UE 120 may perform a reselection from the 5G NR RAT to the legacy RAT to continue to receive wireless service. After the reselection to the legacy RAT, the UE 120 may periodically attempt to perform a reselection from the legacy RAT back to the 5G NR RAT in order to obtain 5G service.

In some implementations, the UE 120 may determine to perform a reselection from the legacy BS 312 associated with a legacy RAT (such as a 2G RAT or a 3G RAT) to the BS 310 associated with a 5G NR RAT. For example, the UE 120 may determine to perform a reselection from a legacy cell of the legacy BS 312 to a 5G cell associated with the BS 310. In some implementations, the UE 120 may determine whether the UE 120 has previously found a 5G cell associated with a 5G NR RAT while registered with the legacy cell of the legacy BS 312. The UE 120 may determine a periodic search time interval for a 5G cell search process based on whether the UE 120 previously found a 5G cell associated with the 5G NR RAT while registered with the legacy cell. In some implementations, the UE 120 may determine whether the legacy cell is included in a 5G cell available list maintained by the UE 120, such as the 5G cell available list 325. The 5G cell available list 325 may include a list of legacy cells that the UE 120 previously found a 5G cell while registered with the corresponding legacy cell. Thus, the UE 120 may determine whether the legacy cell of the legacy BS 312 is included in the 5G cell available list 325 in order to determine whether the UE 120 previously found a 5G cell while registered with the legacy cell. If the 5G cell available list 325 includes the legacy cell associated with the legacy BS 312, then the UE 120 previously found a 5G cell while registered with the legacy cell. For example, the UE 120 may have found a 5G cell of the BS 310 while registered with the legacy cell. If the 5G cell available list 325 does not include the legacy cell associated with the legacy BS 312, the UE 120 may determine whether the legacy cell is included in a 5G cell not available list maintained by the UE 120, such as the 5G cell not available list 326. The 5G cell not available list 326 may include a list of legacy cells that the UE 120 has not previously found a 5G cell while registered with the corresponding legacy cell. Thus, if the 5G cell not available list 326 includes the legacy cell, the UE 120 may determine that the UE 120 has not previously found a 5G cell while registered with the legacy cell. Furthermore, if the legacy cell is not listed in either the 5G cell available list 325 or the 5G cell not available list 326, the UE 120 has not previously searched for a 5G cell while registered with the legacy cell of the legacy BS 312, as further described herein.

In some implementations, the UE 120 may select a first periodic search time interval for the 5G cell search process if the UE 120 previously found a 5G cell associated with the 5G NR RAT while registered with the legacy cell associated with the legacy BS 312. For example, the UE 120 may select the first periodic search time interval for the 5G cell search process if the UE 120 determines that the 5G cell available list 325 includes the legacy cell. In some implementations, the UE 120 may select a second periodic search time interval for the 5G cell search process if UE 120 has not previously found a 5G cell associated with the 5G NR RAT while registered with the legacy cell. For example, the UE 120 may select the second periodic search time interval for the 5G cell search process if the UE 120 determines the 5G cell not available list 326 includes the legacy cell. In some implementations, the UE 120 may select a third periodic search time interval for the 5G cell search process if the UE 120 has not previously searched for a 5G cell associated with the 5G NR RAT while registered with the legacy cell. For example, the UE 120 may select a third periodic search time interval for the 5G cell search process if the UE 120 determines that the legacy cell is not listed in either the 5G cell available list 325 or the 5G cell not available list 326.

In some implementations, the first periodic search time interval may be a shorter time interval than both the second periodic search time interval and the third periodic search time interval. Also, the third periodic search time interval may be a shorter time interval than the second periodic search time interval. In some implementations, the first periodic search time interval may be referred to as a short periodic search time interval, or T_short. The second periodic search time interval may be referred to as a long periodic search time interval, or T_long. The third periodic search time interval may be referred to as a normal periodic search time interval, or T_normal. The T_short may be shorter than the T_normal, and the T_normal may be shorter than the T_long, which may be represented as T_short < T_normal < T_long. In some implementations, the T_short, the T_normal, and the T_long time intervals may be preconfigured and may be configurable. As a non-limiting example, the T_short may be configured to be between a 2–5 minute periodic search time interval, the T_normal may be configured to be between a 10–30 minute periodic search time interval, and the T_long may be configured to be at least a 1 hour periodic search time interval. As another non-limiting example, the T_short may be configured to be between a 1–10 minute periodic search time interval, the T_normal may be configured to be between a 10–45 minute periodic search time interval, and the T_long may be configured to be at least a 45 minute periodic search time interval.

In some implementations, the UE 120 may perform the 5G cell search process based on the selected periodic search time interval to search for a 5G cell associated with the 5G NR RAT. After searching for and finding a 5G cell using the 5G cell search process, the UE 120 may perform a reselection from the legacy cell of the legacy BS 312 to the 5G cell of the BS 310. In some implementations, the 5G cell search process, which also may be referred to as a background 5G cell search process, may be performed while the UE 120 is in an idle mode. In some implementations, the 5G cell search process may be triggered by the selected periodic search time interval while the UE 120 is in an idle mode. For example, the UE 120 may implement a 5G cell search timer that is configured to track the selected periodic search time interval. After the selected periodic search time interval expires, the UE 120 may perform the 5G cell search process. The 5G cell search timer may be paused while the UE 120 performs the 5G cell search process, and may be restarted after the UE 120 completes the 5G cell search process. For example, if the UE 120 does not find a 5G cell after completion of a first 5G cell search process that was triggered after expiration of the selected periodic search time interval, the UE 120 may restart the 5G cell search timer. After the selected periodic search time interval expires, the UE 120 may perform a second 5G cell search process. The UE 120 may continue to perform 5G cell search processes that are triggered by the selected periodic search time interval until the UE 120 finds a 5G cell (such as a 5G cell of the BS 310) .

In some implementations, if the legacy cell of the legacy BS 312 is listed in the 5G cell available list 325, the UE 120 may perform the 5G cell search process using the first periodic search time interval, which may be referred as T_short. Selecting the shortest periodic search time interval when the UE 120 previously found a 5G cell while registered with the legacy cell allows the UE 120 to increase the frequency when the UE 120 performs the 5G cell search process. By shortening the time interval and increasing the frequency of triggering the 5G cell search process, the UE 120 may find a 5G cell quicker than when other time intervals are selected. In some implementations, if the legacy cell of the legacy BS 312 is listed in the 5G cell not available list 326, the UE 120 may perform the 5G cell search process using the second periodic search time interval, which may be referred as T_long. In some implementations, if the UE 120 finds a 5G cell (such as a 5G cell of the BS 310) while performing the 5G cell search process using the second periodic search time interval (such as T_long) , the UE 120 may update the cell lists to remove the legacy cell from the 5G cell not available list 326 and add the legacy cell to the 5G cell available list 325. In some implementations, if the legacy cell of the legacy BS 312 is not listed in either the 5G cell available list 325 or the 5G cell not available list 326, the UE 120 may perform the 5G cell search process using the third periodic search time interval, which may be referred as T_normal. If the UE 120 finds a 5G cell while performing the 5G cell search process using the third periodic search time interval (such as T_normal) , the UE 120 may add the legacy cell to the 5G cell available list 325. Thus, the next time the UE 120 performs a 5G cell search process while the UE 120 is registered to the legacy cell, the UE 120 may select the first periodic search time interval (such as T_short) . If the UE 120 does not find a 5G cell while performing the 5G cell search process using the third periodic search time interval (such as T_normal) , the UE 120 may add the legacy cell to the 5G cell not available list 326. Thus, the next time the UE 120 performs a 5G cell search process while the UE 120 is registered to the legacy cell, the UE 120 may select the second periodic search time interval (such as T_long) .

After performing the 5G cell search process using the selected periodic search time interval and finding a 5G cell (such as a 5G cell of the BS 310) , the UE 120 may perform a reselection from the legacy cell of the legacy BS 312 to the 5G cell of the BS 310. The UE 120 may exchange various messages with the 5G cell of the BS 310 to perform the reselection and register with the 5G cell to receive 5G services. For example, the UE 120 may transmit a registration request message to the 5G cell of the BS 310, and the 5G cell of the BS 310 may respond with a registration accept message.

Figure 4 depicts a flowchart 400 with example operations performed by an apparatus of a UE for selecting a periodic search time interval associated with a 5G cell search process for performing a 5G network reselection from a legacy network.

At block 410, the apparatus of the UE may determine, while the UE is registered with a legacy cell associated with a WWAN legacy RAT, to perform a 5G cell search process to search for a 5G NR RAT. In some implementations, the WWAN legacy RAT (which also may be referred to as a legacy RAT) may include a 2G RAT or a 3G RAT.

At block 420, the apparatus of the UE may determine whether the UE previously found a 5G cell associated with the 5G NR RAT while registered with the legacy cell associated with the WWAN legacy RAT. For example, the apparatus of the UE may determine whether a first cell list (such as a 5G cell available list) maintained by the UE includes the legacy cell.

At block 430, the apparatus of the UE may determine a periodic search time interval for the 5G cell search process based on whether the UE previously found a 5G cell associated with the 5G NR RAT while registered with the legacy cell. For example, the apparatus of the UE may select a first periodic search time interval (such as T_short) for the 5G cell search process in response to determining that first cell list (such as the 5G cell available list) includes the legacy cell. The apparatus of the UE may select a second periodic search time interval (such as T_long) for the 5G cell search process in response to determining that a second cell list (such as a 5G cell not available list) includes the legacy cell. The apparatus of the UE may select a third periodic search time interval (such as T_normal) for the 5G cell search process in response to determining that the first cell list and second cell list do not include the legacy cell.

At block 440, the apparatus of the UE may perform the 5G cell search process based on the periodic search time interval to search for a 5G cell associated with the 5G NR RAT. After searching for and finding a 5G cell, the UE may perform a reselection from the legacy cell of the WWAN legacy RAT to the 5G cell.

Figure 5 depicts a flowchart 500 with example operations performed by an apparatus of a UE for assigning a legacy cell to a cell list associated with a 5G cell search process.

At block 510, the apparatus of the UE may register with a legacy cell of a WWAN legacy RAT. In some implementations, the WWAN legacy RAT may include a 2G RAT or a 3G RAT.

At block 520, the apparatus of the UE may select a periodic search time interval (such as T_normal) for a 5G cell search process in response to determining the legacy cell is not included in either a 5G cell available list or in a 5G cell not available list.

At block 530, the apparatus of the UE may initiate the 5G cell search process after the periodic search time interval (such as T_normal) expires.

At block 540, the apparatus of the UE may determine whether a 5G cell was found during the 5G cell search process.

At block 550, if a 5G cell was found during the 5G cell search process, the apparatus of the UE may add the legacy cell to the 5G cell available list.

At block 560, if a 5G cell was not found during the 5G cell search process, the apparatus of the UE may add the legacy cell to the 5G cell not available list.

Figure 6 shows a block diagram of an example wireless communication apparatus 600. In some implementations, the wireless communication apparatus 600 can be an example of a device for use in a UE, such as the UE 120 described above with reference to Figure 3. In some implementations, the wireless communication apparatus 600 can be an example of a device for use in a BS, such as the BS 310 or the legacy BS 312 described above with reference to Figure 3. The wireless communication apparatus 600 is capable of transmitting (or outputting for transmission) and receiving wireless communications.

The wireless communication apparatus 600 can be, or can include, a chip, system on chip (SoC) , chipset, package or device. The term “system-on-chip” (SoC) is used herein to refer to a set of interconnected electronic circuits typically, but not exclusively, including one or more processors, a memory, and a communication interface. The SoC may include a variety of different types of processors and processor cores, such as a general purpose processor, a central processing unit (CPU) , a digital signal processor (DSP) , a graphics processing unit (GPU) , an accelerated processing unit (APU) , a sub-system processor, an auxiliary processor, a single-core processor, and a multicore processor. The SoC may further include other hardware and hardware combinations, such as a field programmable gate array (FPGA) , a configuration and status register (CSR) , an application-specific integrated circuit (ASIC) , other programmable logic device, discrete gate logic, transistor logic, registers, performance monitoring hardware, watchdog hardware, counters, and time references. SoCs may be integrated circuits (ICs) configured such that the components of the IC reside on the same substrate, such as a single piece of semiconductor material (such as, for example, silicon) .

The term “system in a package” (SIP) is used herein to refer to a single module or package that may contain multiple resources, computational units, cores and/or processors on two or more IC chips, substrates, or SoCs. For example, a SIP may include a single substrate on which multiple IC chips or semiconductor dies are stacked in a vertical configuration. Similarly, the SIP may include one or more multi-chip modules (MCMs) on which multiple ICs or semiconductor dies are packaged into a unifying substrate. A SIP also may include multiple independent SoCs coupled together via high speed communication circuitry and packaged in close proximity, such as on a single motherboard or in a single mobile communication device. The proximity of the SoCs facilitates high speed communications and the sharing of memory and resources.

The term “multicore processor” is used herein to refer to a single IC chip or chip package that contains two or more independent processing cores (for example a CPU core, IP core, GPU core, among other examples) configured to read and execute program instructions. An SoC may include multiple multicore processors, and each processor in an SoC may be referred to as a core. The term “multiprocessor” may be used herein to refer to a system or device that includes two or more processing units configured to read and execute program instructions.

The wireless communication apparatus 600 may include one or more modems 602. In some implementations, the one or more modems 602 (collectively “the modem 602” ) may include a WWAN modem (for example, a 3GPP 4G LTE or 5G compliant modem) . In some implementations, the wireless communication apparatus 600 also includes one or more radios 604 (collectively “the radio 604” ) . In some implementations, the wireless communication apparatus 600 further includes one or more processors, processing blocks or processing elements 606 (collectively “the processor 606” ) and one or more memory blocks or elements 608 (collectively “the memory 608” ) .

The modem 602 can include an intelligent hardware block or device such as, for example, an application-specific integrated circuit (ASIC) among other possibilities. The modem 602 is generally configured to implement a PHY layer. For example, the modem 602 is configured to modulate packets and to output the modulated packets to the radio 604 for transmission over the wireless medium. The modem 602 is similarly configured to obtain modulated packets received by the radio 604 and to demodulate the packets to provide demodulated packets. In addition to a modulator and a demodulator, the modem 602 may further include digital signal processing (DSP) circuitry, automatic gain control (AGC) , a coder, a decoder, a multiplexer and a demultiplexer. For example, while in a transmission mode, data obtained from the processor 606 is provided to a coder, which encodes the data to provide encoded bits. The encoded bits are then mapped to points in a modulation constellation (using a selected MCS) to provide modulated symbols. The modulated symbols may then be mapped to a number NSS of spatial streams or a number NSTS of space-time streams. The modulated symbols in the respective spatial or space-time streams may then be multiplexed, transformed via an inverse fast Fourier transform (IFFT) block, and subsequently provided to the DSP circuitry for Tx windowing and filtering. The digital signals may then be provided to a digital-to-analog converter (DAC) . The resultant analog signals may then be provided to a frequency upconverter, and ultimately, the radio 604. In implementations involving beamforming, the modulated symbols in the respective spatial streams are precoded via a steering matrix prior to their provision to the IFFT block.

While in a reception mode, digital signals received from the radio 604 are provided to the DSP circuitry, which is configured to acquire a received signal, for example, by detecting the presence of the signal and estimating the initial timing and frequency offsets. The DSP circuitry is further configured to digitally condition the digital signals, for example, using channel (narrowband) filtering, analog impairment conditioning (such as correcting for I/Q imbalance) , and applying digital gain to ultimately obtain a narrowband signal. The output of the DSP circuitry may then be fed to the AGC, which is configured to use information extracted from the digital signals, for example, in one or more received training fields, to determine an appropriate gain. The output of the DSP circuitry also is coupled with the demodulator, which is configured to extract modulated symbols from the signal and, for example, compute the logarithm likelihood ratios (LLRs) for each bit position of each subcarrier in each spatial stream. The demodulator is coupled with the decoder, which may be configured to process the LLRs to provide decoded bits. The decoded bits from all of the spatial streams are then fed to the demultiplexer for demultiplexing. The demultiplexed bits may then be descrambled and provided to the MAC layer (the processor 606) for processing, evaluation, or interpretation.

The radio 604 generally includes at least one radio frequency (RF) transmitter (or “transmitter chain” ) and at least one RF receiver (or “receiver chain” ) , which may be combined into one or more transceivers. For example, the RF transmitters and receivers may include various DSP circuitry including at least one power amplifier (PA) and at least one low-noise amplifier (LNA) , respectively. The RF transmitters and receivers may, in turn, be coupled to one or more antennas. For example, in some implementations, the wireless communication apparatus 600 can include, or be coupled with, multiple transmit antennas (each with a corresponding transmit chain) and multiple receive antennas (each with a corresponding receive chain) . The symbols output from the modem 602 are provided to the radio 604, which then transmits the symbols via the coupled antennas. Similarly, symbols received via the antennas are obtained by the radio 604, which then provides the symbols to the modem 602.

The processor 606 can include an intelligent hardware block or device such as, for example, a processing core, a processing block, a central processing unit (CPU) , a microprocessor, a microcontroller, a digital signal processor (DSP) , an application-specific integrated circuit (ASIC) , a programmable logic device (PLD) such as a field programmable gate array (FPGA) , discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. The processor 606 processes information received through the radio 604 and the modem 602, and processes information to be output through the modem 602 and the radio 604 for transmission through the wireless medium. In some implementations, the processor 606 may generally control the modem 602 to cause the modem to perform various operations described above.

The memory 608 can include tangible storage media such as random-access memory (RAM) or read-only memory (ROM) , or combinations thereof. The memory 608 also can store non-transitory processor-or computer-executable software (SW) code containing instructions that, when executed by the processor 606, cause the processor to perform various operations described herein for wireless communication, including the generation, transmission, reception and interpretation of MPDUs, frames or packets. For example, various functions of components disclosed herein, or various blocks or steps of a method, operation, process or algorithm disclosed herein, can be implemented as one or more modules of one or more computer programs.

Figure 7 shows a block diagram of an example mobile communication device 704. For example, the mobile communication device 704 can be an example implementation of the UE 120 described herein. The mobile communication device 704 includes a wireless communication apparatus (WCA) 715. For example, the WCA 715 may be an example implementation of the wireless communication apparatus 600 described with reference to Figure 6. The mobile communication device 704 also includes one or more antennas 725 coupled with the WCA 715 to transmit and receive wireless communications. The mobile communication device 704 additionally includes an application processor 735 coupled with the WCA 715, and a memory 745 coupled with the application processor 735. In some implementations, the mobile communication device 704 further includes a UI 755 (such as a touchscreen or keypad) and a display 765, which may be integrated with the UI 755 to form a touchscreen display. In some implementations, the mobile communication device 704 may further include one or more sensors 775 such as, for example, one or more inertial sensors, accelerometers, temperature sensors, pressure sensors, or altitude sensors. Ones of the aforementioned components can communicate with other ones of the components directly or indirectly, over at least one bus. The mobile communication device 704 further includes a housing that encompasses the WCA 715, the application processor 735, the memory 745, and at least portions of the antennas 725, UI 755, and display 765.

Figures 1–7 and the operations described herein are examples meant to aid in understanding example implementations and should not be used to limit the potential implementations or limit the scope of the claims. Some implementations may perform additional operations, fewer operations, operations in parallel or in a different order, and some operations differently.

The foregoing disclosure provides illustration and description but is not intended to be exhaustive or to limit the aspects to the precise form disclosed. Modifications and variations may be made in light of the above disclosure or may be acquired from practice of the aspects.

As used herein, the term “component” is intended to be broadly construed as hardware, firmware, or a combination of hardware and software. As used herein, a processor is implemented in hardware, firmware, or a combination of hardware and software. As used herein, the phrase “based on” is intended to be broadly construed to mean “based at least in part on. ”

Some aspects are described herein in connection with thresholds. As used herein, satisfying a threshold may refer to a value being greater than the threshold, greater than or equal to the threshold, less than the threshold, less than or equal to the threshold, equal to the threshold, not equal to the threshold, or the like.

As used herein, a phrase referring to “at least one of” or “one or more of” a list of items refers to any combination of those items, including single members. For example, “at least one of: a, b, or c” is intended to cover the possibilities of: a only, b only, c only, a combination of a and b, a combination of a and c, a combination of b and c, and a combination of a and b and c.

The various illustrative components, logic, logical blocks, modules, circuits, operations and algorithm processes described in connection with the implementations disclosed herein may be implemented as electronic hardware, firmware, software, or combinations of hardware, firmware or software, including the structures disclosed in this specification and the structural equivalents thereof. The interchangeability of hardware, firmware and software has been described generally, in terms of functionality, and illustrated in the various illustrative components, blocks, modules, circuits and processes described above. Whether such functionality is implemented in hardware, firmware or software depends upon the particular application and design constraints imposed on the overall system.

The hardware and data processing apparatus used to implement the various illustrative components, logics, logical blocks, modules and circuits described in connection with the aspects disclosed herein may be implemented or performed with a general purpose single-or multi-chip processor, a digital signal processor (DSP) , an application specific integrated circuit (ASIC) , a field programmable gate array (FPGA) or other programmable logic device (PLD) , discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, or, any conventional processor, controller, microcontroller, or state machine. A processor also may be implemented as a combination of computing devices, for example, a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. In some implementations, particular processes, operations and methods may be performed by circuitry that is specific to a given function.

As described above, in some aspects implementations of the subject matter described in this specification can be implemented as software. For example, various functions of components disclosed herein, or various blocks or steps of a method, operation, process or algorithm disclosed herein can be implemented as one or more modules of one or more computer programs. Such computer programs can include non-transitory processor-or computer-executable instructions encoded on one or more tangible processor-or computer-readable storage media for execution by, or to control the operation of, data processing apparatus including the components of the devices described herein. By way of example, and not limitation, such storage media may include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that may be used to store program code in the form of instructions or data structures. Combinations of the above should also be included within the scope of storage media.

Various modifications to the implementations described in this disclosure may be readily apparent to persons having ordinary skill in the art, and the generic principles defined herein may be applied to other implementations without departing from the spirit or scope of this disclosure. Thus, the claims are not intended to be limited to the implementations shown herein but are to be accorded the widest scope consistent with this disclosure, the principles and the novel features disclosed herein.

Additionally, various features that are described in this specification in the context of separate implementations also can be implemented in combination in a single implementation. Conversely, various features that are described in the context of a single implementation also can be implemented in multiple implementations separately or in any suitable subcombination. As such, although features may be described above as acting in particular combinations, and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. Further, the drawings may schematically depict one or more example processes in the form of a flowchart or flow diagram. However, other operations that are not depicted can be incorporated in the example processes that are schematically illustrated. For example, one or more additional operations can be performed before, after, simultaneously, or between any of the illustrated operations. In some circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products. Additionally, other implementations are within the scope of the following claims. In some cases, the actions recited in the claims can be performed in a different order and still achieve desirable results.

Claims

A method for wireless communication performed by an apparatus of a user equipment (UE) , comprising:

determining, while the UE is registered with a legacy cell associated with a wireless wide area network (WWAN) legacy radio access technology (RAT) , to perform a 5G cell search process to search for a 5G New Radio (NR) RAT;

determining whether the UE previously found a 5G cell associated with the 5G NR RAT while registered with the legacy cell associated with the WWAN legacy RAT;

determining a periodic search time interval for the 5G cell search process based on whether the UE previously found a 5G cell associated with the 5G NR RAT while registered with the legacy cell; and

performing the 5G cell search process based on the periodic search time interval to search for a 5G cell associated with the 5G NR RAT.
The method of claim 1, wherein determining whether the UE previously found a 5G cell associated with the 5G NR RAT while registered with the legacy cell comprises:

determining whether a first cell list maintained by the UE includes the legacy cell; and

determining that the UE previously found a 5G cell associated with the 5G NR RAT while registered with the legacy cell in response to determining that the first cell list includes the legacy cell.
The method of claim 2, further comprising:

determining whether a second cell list maintained by the UE includes the legacy cell in response to determining that the first cell list does not includes the legacy cell; and

determining that the UE has not previously found a 5G cell associated with the 5G NR RAT while registered with the legacy cell in response to determining that the second cell list includes the legacy cell.
The method of claim 3, wherein determining the periodic search time interval for the 5G cell search process based on whether the UE previously found a 5G cell associated with the 5G NR RAT while registered with the legacy cell comprises:

selecting a first periodic search time interval for the 5G cell search process in response to determining that the first cell list includes the legacy cell; and

selecting a second periodic search time interval for the 5G cell search process in response to determining that the second cell list includes the legacy cell,

wherein the first periodic search time interval is a shorter time interval than the second periodic search time interval.
The method of claim 4, wherein performing the 5G cell search process based on the periodic search time interval comprises:

performing the 5G cell search process based on the first periodic search time interval in response to determining that the first cell list includes the legacy cell; or

performing the 5G cell search process based on the second periodic search time interval in response to determining that the second cell list includes the legacy cell.
The method of claim 4, wherein the first cell list is a 5G cell available list maintained by the UE, and the second cell list is a 5G cell not available list maintained by the UE.
The method of claim 4, further comprising:

determining that the UE has not previously searched for a 5G cell associated with the 5G NR RAT while registered with the legacy cell in response to determining that the first cell list and the second cell list do not includes the legacy cell; and

selecting a third periodic search time interval for the 5G cell search process in response to determining that the first cell list and the second cell list do not include the legacy cell,

wherein the first periodic search time interval is a shorter time interval than the third periodic search time interval, and the third periodic search time interval is a shorter time interval than the second periodic search time interval.
The method of claim 7, further comprising:

performing the 5G cell search process based on the third periodic search time interval in response to determining that the UE has not previously searched for a 5G cell associated with the 5G NR RAT while registered with the legacy cell;

adding the legacy cell to the first cell list in response to finding a 5G cell associated with the 5G NR RAT using the 5G cell search process; and

adding the legacy cell to the second cell list in response to not finding a 5G cell associated with the 5G NR RAT using the 5G cell search process.
The method of claim 1, wherein the WWAN legacy RAT includes a 2G RAT or a 3G RAT.
The method of claim 1, wherein performing the 5G cell search process based on the periodic search time interval further comprises:

performing the 5G cell search process after expiration of the periodic search time interval.
The method of claim 1, wherein the 5G cell search process is a background 5G cell search process performed by the UE during an idle mode.
The method of claim 1, further comprising:

performing a reselection from the WWAN legacy RAT to the 5G NR RAT in response to searching and finding a 5G cell associated with the 5G NR RAT.
The method of claim 1, wherein determining the periodic search time interval for the 5G cell search process based on whether the UE previously found a 5G cell associated with the 5G NR RAT while registered with the legacy cell further comprises:

selecting a first periodic search time interval for the 5G cell search process in response to determining that the UE previously found a 5G cell associated with the 5G NR RAT while registered with the legacy cell; and

selecting a second periodic search time interval for the 5G cell search process in response to determining that the UE has not previously found a 5G cell associated with the 5G NR RAT while registered with the legacy cell,

wherein the first periodic search time interval is a shorter time interval than the second periodic search time interval.
The method of claim 13, further comprising:

determining that the UE has not previously searched for a 5G cell associated with the 5G NR RAT while registered with the legacy cell; and

selecting a third periodic search time interval for the 5G cell search process in response to determining that the UE has not previously searched for a 5G cell associated with the 5G NR RAT while registered with the legacy cell,

wherein the first periodic search time interval is a shorter time interval than the third periodic search time interval, and the third periodic search time interval is a shorter time interval than the second periodic search time interval.
An apparatus of a user equipment (UE) for wireless communication, comprising:

one or more interfaces for communicating via a wireless communication network; and

one or more processors configured to perform any one of the method claims 1–14.
A computer-readable medium having stored therein instructions which, when executed by a processor of a user equipment (UE) , causes the UE to perform any

one of the method claims 1–14.
An apparatus, comprising:

means for implementing any one of the method claims 1–14.