WO2021184237A1

WO2021184237A1 - Dynamic base station selection

Info

Publication number: WO2021184237A1
Application number: PCT/CN2020/079893
Authority: WO
Inventors: Xiaomin Dong; Hao Zhang; Jian Li; Aimin SHANG
Original assignee: Qualcomm Incorporated
Priority date: 2020-03-18
Filing date: 2020-03-18
Publication date: 2021-09-23

Abstract

This disclosure provides systems, methods and apparatus, including computer programs encoded on computer storage media, for cell selection. In one aspect, a wireless device may detect one or more synchronization signal blocks (SSBs) broadcast by one or more base stations and select a first base station of the one or more base stations based on a first selection criteria. The wireless device may determine whether a tracking area code (TAC) associated with the first base station is associated with a forbidden tracking area code (FTAC) list and may selectively transmit a registration request to a second base station of the one or more base stations based at least in part on the determination.

Description

DYNAMIC BASE STATION SELECTION

TECHNICAL FIELD

This disclosure relates generally to wireless communication and, more specifically, to dynamic base station selection in wireless communication systems.

DESCRIPTION OF THE RELATED TECHNOLOGY

Wireless communication systems are widely deployed to provide various telecommunication services such as telephony, video, data, messaging, and broadcasts. Typical wireless communication systems may employ multiple-access technologies capable of supporting communication with multiple users by sharing available system resources. Examples of such multiple-access technologies include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, single-carrier frequency division multiple access (SC-FDMA) systems, and time division synchronous code division multiple access (TD-SCDMA) systems.

These multiple access technologies have been adopted in various telecommunication standards to provide a common protocol that enables different wireless devices to communicate on a municipal, national, regional, and even global level. An example telecommunication standard is 5G New Radio (NR) , which is part of a continuous mobile broadband evolution promulgated by Third Generation Partnership Project (3GPP) to meet new requirements associated with latency, reliability, security, scalability (such as with Internet of Things (IoT) ) , and other requirements. 5G NR includes services associated with enhanced mobile broadband (eMBB) , massive machine type communications (mMTC) , and ultra-reliable low latency communications (URLLC) . Some aspects of 5G NR may be based on the 4G Long Term Evolution (LTE) standard. There exists a need for further improvements in 5G NR technology.

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 as a method of wireless communication. The method can be performed by a wireless device for purposes of registering with a base station. In some implementations, the method can include detecting one or more synchronization signal blocks (SSBs) broadcast by one or more base stations while connected to a current base station; selecting a first base station of the one or more base stations based on a first selection criteria; determining whether a tracking area code (TAC) associated with the first base station is associated with a forbidden tracking area code (FTAC) list; and selectively transmitting a registration request to a second base station of the one or more base stations based at least in part on the determination.

In some implementations, selecting the first base station may include determining a signal strength of each SSB broadcast by the one or more base stations. For example, the first selection criteria may include the signal strengths of the SSBs. In some implementations, selecting the first base station may further include determining that the SSBs broadcast by the first base station having greater signal strengths than the SSBs broadcast by the second base station.

In some implementations, selectively transmitting the registration request may include steps of determining that the TAC associated with the first base station is associated with the FTAC list; selecting the second base station, based on the first selection criteria, among the one or more base stations not including the first base station; determining that a TAC associated with the second base station is not associated with the FTAC list; and transmitting the registration request to the second base station in lieu of the first base station. In some implementations, selecting the second base station may include steps of determining a signal strength of each SSB broadcast by the one or more base stations; and determining that the SSBs broadcast by the second base station have greater signal strengths than the SSBs broadcast by other base stations of the one or more base stations not including the first base station.

In some implementations, selectively transmitting the registration request may include steps of determining that the TAC associated with the first base station is associated with the FTAC list; selecting the second base station, based on the first selection criteria, among the one or more base stations not including the first base station; determining that a TAC associated with the second base station also is associated with the FTAC list; selecting a third base station, based on the first selection criteria, among the one or more base stations not including the first and second base stations; determining that a TAC associated with the third base station is not associated with the FTAC list; and transmitting the registration request to the third base station in lieu of the first and second base stations.

In some implementations, selecting the second base station may include steps of determining a signal strength of each SSB broadcast by the one or more base stations; and determining that the SSBs broadcast by the second base station have greater signal strengths than the SSBs broadcast by the third base station. In some implementations, selecting the third base station may include determining that the SSBs broadcast by the third base station have greater signal strengths than the SSBs broadcast by other base station of the one or more base stations not including the first and second base stations.

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 shows a diagram of an example wireless communications system and an access network.

Figures 2A, 2B, 2C, and 2D show examples of a first 5G/NR frame, downlink (DL) channels within a 5G/NR slot, a second 5G/NR frame, and uplink (UL) channels within a 5G/NR slot, respectively.

Figure 3 shows a block diagram of an example base station and user equipment (UE) in an access network.

Figure 4 shows a sequence diagram illustrating an example message exchange between a UE and a number of base stations.

Figure 5 shows an illustrative flowchart depicting an example wireless communication operation.

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

DETAILED DESCRIPTION

The following description is directed to some particular implementations for the purposes of describing 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 described implementations can be implemented in any device, system or network that is capable of transmitting and receiving radio frequency (RF) signals according to one or more of the Long Term Evolution (LTE) , 3G, 4G or 5G (New Radio (NR) ) standards promulgated by the 3rd Generation Partnership Project (3GPP) , the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standards, the IEEE 802.15 standards, or the

standards as defined by the Bluetooth Special Interest Group (SIG) , among others. The described implementations can be implemented in any device, system or network that is capable of transmitting and receiving RF signals according to one or more of the following technologies or techniques: code division multiple access (CDMA) , time division multiple access (TDMA) , frequency division multiple access (FDMA) , orthogonal FDMA (OFDMA) , single-carrier FDMA (SC-FDMA) , single-user (SU) multiple-input multiple-output (MIMO) and multi-user (MU) MIMO. The described implementations also can be implemented using other wireless communication protocols or RF signals suitable for use in one or more of a wireless wide area network (WWAN) , a wireless personal area network (WPAN) , a wireless local area network (WLAN) , or an internet of things (IOT) network.

A user equipment (UE) may discover one or more base stations in its vicinity using a cell search operation. During the cell search operation, the UE detects one or more synchronization signal blocks (SSBs) broadcast by each of the base stations in its vicinity. A UE may be in the coverage area of multiple cells or base stations at any given time. The UE may subsequently perform a cell selection (or reselection) operation to select one of the discovered base stations to register to. During the cell selection operation, the UE may compare one or more features of each base station and select a base station that satisfies a given selection criteria. For example, in some aspects, the UE may compare the signal strengths of the SSBs broadcast by each base station and select the base station with the highest or greatest signal strength.

Base stations may be logically grouped into one or more tracking areas (TAs) based, at least in part, on their geographic locations. Each base station may indicate the TA to which it belongs using a tracking area code (TAC) . The TAC may be included in the SSB (or PBCH) broadcast by each base station. Each UE also may maintain a forbidden tracking area code (FTAC) list that identifies one or more TACs or TAs in which the UE may not operate. If, during the cell selection operation, the UE selects a base station associated with a TAC on the FTAC list, the UE will not register to the selected base station. UEs operating in accordance with existing 3GPP standards may terminate the cell selection operation in response to selecting a base station having a TAC associated with the FTAC list. For example, such UEs may remain connected to their current base stations or attempt to register to another base station during a subsequent cell search or selection operation. In some instances, this may delay or prevent a UE from registering to a base station configured for improved radio access technologies (such as 5G NR) .

Implementations of the subject matter described in this disclosure may be used for dynamically selecting one or more base stations during a cell selection or resection operation. In some implementations, a user equipment (UE) located in the coverage areas of multiple base stations may select one of the base stations that meets a given selection criteria and is associated with a tracking area code (TAC) that is not associated with a forbidden tracking are code (FTAC) list. More specifically, the UE may dynamically or iteratively select a new base station, based on the selection criteria, when the UE determines that the selected base station is associated with a TAC on the FTAC list. When the UE selects a base station associated with a TAC that is not on the FTAC list, the UE may terminate the cell selection operation and attempt to register to the selected base station.

Particular implementations of the subject matter described in this disclosure can be implemented to realize one or more of the following potential advantages. By dynamically selecting one or more base stations during a cell selection operation, aspects of the present disclosure may ensure that the UE is connected to an optimal base station at any given time. For example, rather than terminate the cell search operation responsive to selecting a base station having a TAC associated with the FTAC list, the UE may proceed to analyze the TACs of one or more additional base stations during the same cell selection operation. This may allow the UE to more quickly discover and connect to a suitable base station or a base station with improved capabilities (such as a base station configured for 5G NR) .

Several aspects of telecommunication systems will now be presented with reference to various apparatus and methods. These apparatus and methods will be described in the following detailed description and illustrated in the accompanying drawings by various blocks, components, circuits, processes, algorithms, etc. (collectively referred to as “elements” ) . These elements may be implemented using electronic hardware, computer software, or any combination thereof. Whether such elements are implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system.

By way of example, an element, or any portion of an element, or any combination of elements may be implemented as a “processing system” that includes one or more processors. Examples of processors include microprocessors, microcontrollers, graphics processing units (GPUs) , central processing units (CPUs) , application processors, digital signal processors (DSPs) , reduced instruction set computing (RISC) processors, systems on a chip (SoC) , baseband processors, field programmable gate arrays (FPGAs) , programmable logic devices (PLDs) , state machines, gated logic, discrete hardware circuits, and other suitable hardware configured to perform the various functionality described throughout this disclosure. One or more processors in the processing system may execute software. Software shall be construed broadly to mean instructions, instruction sets, code, code segments, program code, programs, subprograms, software components, applications, software applications, software packages, routines, subroutines, objects, executables, threads of execution, procedures, functions, etc., whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise.

Accordingly, in one or more example implementations, the functions described may be implemented in hardware, software, or any combination thereof. If implemented in software, the functions may be stored on or encoded as one or more instructions or code on a computer-readable medium. Computer-readable media includes computer storage media. Storage media may be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can include a random-access memory (RAM) , a read-only memory (ROM) , an electrically erasable programmable ROM (EEPROM) , optical disk storage, magnetic disk storage, other magnetic storage devices, combinations of the aforementioned types of computer-readable media, or any other medium that can be used to store computer executable code in the form of instructions or data structures that can be accessed by a computer.

Figure 1 shows a diagram of an example wireless communications system and an access network 100. The wireless communications system (also referred to as a wireless wide area network (WWAN) ) includes base stations 102, UEs 104, an Evolved Packet Core (EPC) 160, and another core network 190 (such as a 5G Core (5GC) ) . The base stations 102 may include macrocells (high power cellular base station) or small cells (low power cellular base station) . The macrocells include base stations. The small cells include femtocells, picocells, and microcells.

The base stations 102 configured for 4G LTE (collectively referred to as Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (E-UTRAN) ) may interface with the EPC 160 through backhaul links 132 (such as S1 interface) . The base stations 102 configured for 5G NR (collectively referred to as Next Generation RAN (NG-RAN) ) may interface with core network 190 through backhaul links 184. In addition to other functions, the base stations 102 may perform one or more of the following functions: transfer of user data, radio channel ciphering and deciphering, integrity protection, header compression, mobility control functions (such as handover, dual connectivity) , inter-cell interference coordination, connection setup and release, load balancing, distribution for non-access stratum (NAS) messages, NAS node selection, synchronization, radio access network (RAN) sharing, multimedia broadcast multicast service (MBMS) , subscriber and equipment trace, RAN information management (RIM) , paging, positioning, and delivery of warning messages. The base stations 102 may communicate directly or indirectly (such as through the EPC 160 or core network 190) with each other over backhaul links 134 (such as an X2 interface) . The backhaul links 134 may be wired or wireless.

The base stations 102 may wirelessly communicate with the UEs 104. Each of the base stations 102 may provide communication coverage for a respective geographic coverage area 110. There may be overlapping geographic coverage areas 110. For example, the small cell 102' may have a coverage area 110' that overlaps the coverage area 110 of one or more macro base stations 102. A network that includes both small cell and macrocells may be known as a heterogeneous network. A heterogeneous network also may include Home Evolved Node Bs (eNBs) (HeNBs) , which may provide service to a restricted group known as a closed subscriber group (CSG) . The communication links 120 between the base stations 102 and the UEs 104 may include uplink (UL) (also referred to as reverse link) transmissions from a UE 104 to a base station 102 or downlink (DL) (also referred to as forward link) transmissions from a base station 102 to a UE 104. The communication links 120 may use multiple-input and multiple-output (MIMO) antenna technology, including spatial multiplexing, beamforming, or transmit diversity. The communication links may be through one or more carriers. The base stations 102 /UEs 104 may use spectrum up to Y MHz (such as 5, 10, 15, 20, 100, 400, 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. The carriers may or may not be adjacent to each other. Allocation of carriers may be asymmetric with respect to DL and UL (such as more or fewer carriers may be allocated for DL than for UL) . The component carriers may include a primary component carrier and one or more secondary component carriers. A primary component carrier may be referred to as a primary cell (PCell) and a secondary component carrier may be referred to as a secondary cell (SCell) .

Some UEs 104 may communicate with each other using device-to-device (D2D) communication link 158. The D2D communication link 158 may use the DL/UL WWAN spectrum. The D2D communication link 158 may use one or more sidelink channels, such as a physical sidelink broadcast channel (PSBCH) , a physical sidelink discovery channel (PSDCH) , a physical sidelink shared channel (PSSCH) , and a physical sidelink control channel (PSCCH) . 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 IEEE 802.11 standard, LTE, or NR.

The wireless communications system may further include a Wi-Fi access point (AP) 150 in communication with Wi-Fi stations (STAs) 152 via communication links 154 in a 5 GHz unlicensed frequency spectrum. When communicating in an unlicensed frequency spectrum, the STAs 152 /AP 150 may perform a clear channel assessment (CCA) prior to communicating in order to determine whether the channel is available.

The small cell 102' may operate in a licensed or an unlicensed frequency spectrum. When operating in an unlicensed frequency spectrum, the small cell 102' may employ NR and use the same 5 GHz unlicensed frequency spectrum as used by the Wi-Fi AP 150. The small cell 102', employing NR in an unlicensed frequency spectrum, may boost coverage to or increase capacity of the access network.

A base station 102, whether a small cell 102' or a large cell (such as macro base station) , may include an eNB, gNodeB (gNB) , or another type of base station. Some base stations, such as gNB 180, may operate in a traditional sub 6 GHz spectrum, in millimeter wave (mmW) frequencies, or near mmW frequencies in communication with the UE 104. When the gNB 180 operates in mmW or near mmW frequencies, the gNB 180 may be referred to as a millimeter wave or mmW base station. Extremely high frequency (EHF) is part of the RF in the electromagnetic spectrum. EHF has a range of 30 GHz to 300 GHz and a wavelength between 1 millimeter and 10 millimeters. Radio waves in the band may be referred to as a millimeter wave. Near mmW may extend down to a frequency of 3 GHz with a wavelength of 100 millimeters. The super high frequency (SHF) band extends between 3 GHz and 30 GHz, also referred to as centimeter wave. Communications using the mmW /near mmW radio frequency band (such as 3 GHz –300 GHz) has extremely high path loss and a short range. The mmW base station 180 may utilize beamforming 182 with the UE 104 to compensate for the extremely high path loss and short range.

The base station 180 may transmit a beamformed signal to the UE 104 in one or more transmit directions 182'. The UE 104 may receive the beamformed signal from the base station 180 in one or more receive directions 182”. The UE 104 also may transmit a beamformed signal to the base station 180 in one or more transmit directions. The base station 180 may receive the beamformed signal from the UE 104 in one or more receive directions. The base station 180 /UE 104 may perform beam training to determine the best receive and transmit directions for each of the base station 180 /UE 104. The transmit and receive directions for the base station 180 may or may not be the same. The transmit and receive directions for the UE 104 may or may not be the same.

The EPC 160 may include a Mobility Management Entity (MME) 162, other MMEs 164, a Serving Gateway 166, a Multimedia Broadcast Multicast Service (MBMS) Gateway 168, a Broadcast Multicast Service Center (BM-SC) 170, and a Packet Data Network (PDN) Gateway 172. The MME 162 may be in communication with a Home Subscriber Server (HSS) 174. The MME 162 is the control node that processes the signaling between the UEs 104 and the EPC 160. Generally, the MME 162 provides bearer and connection management. All user Internet protocol (IP) packets are transferred through the Serving Gateway 166, which itself is connected to the PDN Gateway 172. The PDN Gateway 172 provides UE IP address allocation as well as other functions. The PDN Gateway 172 and the BM-SC 170 are connected to the IP Services 176. The IP Services 176 may include the Internet, an intranet, an IP Multimedia Subsystem (IMS) , a PS Streaming Service, or other IP services. The BM-SC 170 may provide functions for MBMS user service provisioning and delivery. The BM-SC 170 may serve as an entry point for content provider MBMS transmission, may be used to authorize and initiate MBMS Bearer Services within a public land mobile network (PLMN) , and may be used to schedule MBMS transmissions. The MBMS Gateway 168 may be used to distribute MBMS traffic to the base stations 102 belonging to a Multicast Broadcast Single Frequency Network (MBSFN) area broadcasting a particular service, and may be responsible for session management (start/stop) and for collecting eMBMS related charging information.

The core network 190 may include an Access and Mobility Management Function (AMF) 192, other AMFs 193, a Session Management Function (SMF) 194, and a User Plane Function (UPF) 195. The AMF 192 may be in communication with a Unified Data Management (UDM) 196. The AMF 192 is the control node that processes the signaling between the UEs 104 and the core network 190. Generally, the AMF 192 provides QoS flow and session management. All user Internet protocol (IP) packets are transferred through the UPF 195. The UPF 195 provides UE IP address allocation as well as other functions. The UPF 195 is connected to the IP Services 197. The IP Services 197 may include the Internet, an intranet, an IP Multimedia Subsystem (IMS) , a PS Streaming Service, or other IP services.

The base station also may be referred to as a gNB, Node B, evolved Node B (eNB) , an access point, a base transceiver station, a radio base station, a radio transceiver, a transceiver function, a basic service set (BSS) , an extended service set (ESS) , a transmit reception point (TRP) , or some other suitable terminology. The base station 102 provides an access point to the EPC 160 or core network 190 for a UE 104. Examples of UEs 104 include a cellular phone, a smart phone, a session initiation protocol (SIP) phone, a laptop, a personal digital assistant (PDA) , a satellite radio, a global positioning system, a multimedia device, a video device, a digital audio player (such as an MP3 player) , a camera, a game console, a tablet, a smart device, a wearable device, a vehicle, an electric meter, a gas pump, a large or small kitchen appliance, a healthcare device, an implant, a sensor/actuator, a display, or any other similar functioning device. Some of the UEs 104 may be referred to as IoT devices (such as a parking meter, gas pump, toaster, vehicles, heart monitor, etc. ) . The UE 104 also may be referred to as a station, a mobile station, a subscriber station, a mobile unit, a subscriber unit, a wireless unit, a remote unit, a mobile device, a wireless device, a wireless communications device, a remote device, a mobile subscriber station, an access terminal, a mobile terminal, a wireless terminal, a remote terminal, a handset, a user agent, a mobile client, a client, or some other suitable terminology.

Figure 2A shows an example of a first slot 200 within a 5G/NR frame structure. Figure 2B shows an example of DL channels 230 within a 5G/NR slot. Figure 2C shows an example of a second slot 250 within a 5G/NR frame structure. Figure 2D shows an example of UL channels 280 within a 5G/NR slot. The 5G/NR frame structure may be FDD in which, for a particular set of subcarriers (carrier system bandwidth) , slots within the set of subcarriers are dedicated for either DL or UL In other cases, the 5G/NR frame structure may be TDD in which, for a particular set of subcarriers (carrier system bandwidth) , slots within the set of subcarriers are dedicated for both DL and UL. In the examples shown in Figures 2A and 2C, the 5G/NR frame structure is configured as TDD, with slot 4 being configured with slot format 28 (with mostly DL) , where D indicates DL, U indicates UL, and X indicates that the slot is flexible for use between DL/UL, and slot 3 being configured with slot format 34 (with mostly UL) . While

slots

3 and 4 are shown with slot formats 34 and 28, respectively, any particular slot may be configured with any of the various available slot formats 0–61.

Slot formats

0 and 1 are all DL and all UL, respectively. Other slot formats 2–61 include a mix of DL, UL, and flexible symbols. UEs are configured with the slot format (dynamically through DL control information (DCI) , or semi-statically/statically through radio resource control (RRC) signaling) through a received slot format indicator (SFI) . This format also may apply to a 5G/NR frame structure that is FDD.

Other wireless communication technologies may have a different frame structure or different channels. A frame (such as 10 milliseconds (ms) ) may be divided into 10 equally sized subframes (1 ms) . Each subframe may include one or more time slots. Subframes also may include mini-slots, which may include 7, 4, or 2 symbols. Each slot may include 7 or 14 symbols, depending on the slot configuration. For slot configuration 0, each slot may include 14 symbols, and for slot configuration 1, each slot may include 7 symbols. The symbols on DL may be cyclic prefix (CP) OFDM (CP-OFDM) symbols. The symbols on UL may be CP-OFDM symbols (for high throughput scenarios) or discrete Fourier transform (DFT) spread OFDM (DFT-s-OFDM) symbols (also referred to as single carrier frequency-division multiple access (SC-FDMA) symbols) (for power limited scenarios; limited to a single stream transmission) . The number of slots within a subframe is based on the slot configuration and the numerology. For slot configuration 0, different numerologies μ 0 to 5 allow for 1, 2, 4, 8, 16, and 32 slots, respectively, per subframe. For slot configuration 1, different numerologies 0 to 2 allow for 2, 4, and 8 slots, respectively, per subframe. Accordingly, for slot configuration 0 and numerology μ, there are 14 symbols/slot and 2μ slots/subframe. The subcarrier spacing and symbol length/duration are a function of the numerology. The subcarrier spacing may be equal to 2^μ*15 kHz, where μ is the numerology 0 to 5. As such, the numerology μ=0 has a subcarrier spacing of 15 kHz and the numerology μ=5 has a subcarrier spacing of 480 kHz. The symbol length/duration is inversely related to the subcarrier spacing. Figures 2A-2D provide an example of slot configuration 0 with 14 symbols per slot and numerology μ=0 with 1 slot per subframe. The subcarrier spacing is 15 kHz and symbol duration is approximately 66.7 microseconds (μs) .

A resource grid may be used to represent the frame structure. Each time slot includes a resource block (RB) (also referred to as a physical RB (PRB) ) that extends across 12 consecutive subcarriers and across a number of symbols. The intersections of subcarriers and symbols of the RB define multiple resource elements (REs) . The number of bits carried by each RE depends on the modulation scheme.

As illustrated in Figure 2A, some of the REs carry a reference (pilot) signal (RS) for the UE. In some configurations, one or more REs may carry a demodulation RS (DM-RS) (indicated as Rx for one particular configuration, where 100x is the port number, but other DM-RS configurations are possible) . In some configurations, one or more REs may carry a channel state information reference signal (CSI-RS) for channel measurement at the UE. The REs also may include a beam measurement RS (BRS) , a beam refinement RS (BRRS) , and a phase tracking RS (PT-RS) .

Figure 2B illustrates an example of various DL channels within a subframe of a frame. The physical downlink control channel (PDCCH) carries DCI within one or more control channel elements (CCEs) , each CCE including nine RE groups (REGs) , each REG including four consecutive REs in an OFDM symbol. A primary synchronization signal (PSS) may be within symbol 2 of particular subframes of a frame. The PSS is used by a UE 104 to determine subframe or symbol timing and a physical layer identity. A secondary synchronization signal (SSS) may be within symbol 4 of particular subframes of a frame. The SSS is used by a UE to determine a physical layer cell identity group number and radio frame timing. Based on the physical layer identity and the physical layer cell identity group number, the UE can determine a physical cell identifier (PCI) . Based on the PCI, the UE can determine the locations of the aforementioned DM-RS. The physical broadcast channel (PBCH) , which carries a master information block (MIB) , may be logically grouped with the PSS and SSS to form a synchronization signal (SS) /PBCH block. The MIB provides a number of RBs in the system bandwidth and a system frame number (SFN) . The physical downlink shared channel (PDSCH) carries user data, broadcast system information not transmitted through the PBCH such as system information blocks (SIBs) , and paging messages.

As illustrated in Figure 2C, some of the REs carry DM-RS (indicated as R for one particular configuration, but other DM-RS configurations are possible) for channel estimation at the base station. The UE may transmit DM-RS for the physical uplink control channel (PUCCH) and DM-RS for the physical uplink shared channel (PUSCH) . The PUSCH DM-RS may be transmitted in the first one or two symbols of the PUSCH. The PUCCH DM-RS may be transmitted in different configurations depending on whether short or long PUCCHs are transmitted and depending on the particular PUCCH format used. Although not shown, the UE may transmit sounding reference signals (SRS) . The SRS may be used by a base station for channel quality estimation to enable frequency-dependent scheduling on the UL.

Figure 2D illustrates an example of various UL channels within a subframe of a frame. The PUCCH may be located as indicated in one configuration. The PUCCH carries uplink control information (UCI) , such as scheduling requests, a channel quality indicator (CQI) , a precoding matrix indicator (PMI) , a rank indicator (RI) , and HARQ ACK/NACK feedback. The PUSCH carries data, and may additionally be used to carry a buffer status report (BSR) , a power headroom report (PHR) , or UCI.

Figure 3 shows a block diagram of an example base station 310 and UE 350 in an access network. With reference for example to Figure 1, in the DL, IP packets from the EPC 160 may be provided to a controller/processor 375. The controller/processor 375 implements layer 3 and layer 2 functionality. Layer 3 includes a radio resource control (RRC) layer, and layer 2 includes a service data adaptation protocol (SDAP) layer, a packet data convergence protocol (PDCP) layer, a radio link control (RLC) layer, and a medium access control (MAC) layer. The controller/processor 375 provides RRC layer functionality associated with broadcasting of system information (such as MIB, SIBs) , RRC connection control (such as RRC connection paging, RRC connection establishment, RRC connection modification, and RRC connection release) , inter radio access technology (RAT) mobility, and measurement configuration for UE measurement reporting; PDCP layer functionality associated with header compression /decompression, security (ciphering, deciphering, integrity protection, integrity verification) , and handover support functions; RLC layer functionality associated with the transfer of upper layer packet data units (PDUs) , error correction through ARQ, concatenation, segmentation, and reassembly of RLC service data units (SDUs) , re-segmentation of RLC data PDUs, and reordering of RLC data PDUs; and MAC layer functionality associated with mapping between logical channels and transport channels, multiplexing of MAC SDUs onto transport blocks (TBs) , demultiplexing of MAC SDUs from TBs, scheduling information reporting, error correction through HARQ, priority handling, and logical channel prioritization.

The transmit (TX) processor 316 and the receive (RX) processor 370 implement layer 1 functionality associated with various signal processing functions. Layer 1, which includes a physical (PHY) layer, may include error detection on the transport channels, forward error correction (FEC) coding/decoding of the transport channels, interleaving, rate matching, mapping onto physical channels, modulation/demodulation of physical channels, and MIMO antenna processing. The TX processor 316 handles mapping to signal constellations based on various modulation schemes (such as binary phase-shift keying (BPSK) , quadrature phase-shift keying (QPSK) , M-phase-shift keying (M-PSK) , M-quadrature amplitude modulation (M-QAM) ) . The coded and modulated symbols may then be split into parallel streams. Each stream may then be mapped to an OFDM subcarrier, multiplexed with a reference signal (or pilot) in the time or frequency domain, and then combined together using an Inverse Fast Fourier Transform (IFFT) to produce a physical channel carrying a time domain OFDM symbol stream. The OFDM stream is spatially pre-coded to produce multiple spatial streams. Channel estimates from a channel estimator 374 may be used to determine the coding and modulation scheme, as well as for spatial processing. The channel estimate may be derived from a reference signal or channel condition feedback transmitted by the UE 350. Each spatial stream may then be provided to a different antenna 320 via a separate transmitter 318TX. Each transmitter 318TX may modulate an RF carrier with a respective spatial stream for transmission.

At the UE 350, each receiver 354RX receives a signal through its respective antenna 352. Each receiver 354RX recovers information modulated onto an RF carrier and provides the information to the receive (RX) processor 356. The TX processor 368 and the RX processor 356 implement layer 1 functionality associated with various signal processing functions. The RX processor 356 may perform spatial processing on the information to recover any spatial streams destined for the UE 350. If multiple spatial streams are destined for the UE 350, they may be combined by the RX processor 356 into a single OFDM symbol stream. The RX processor 356 then converts the OFDM symbol stream from the time-domain to the frequency domain using a Fast Fourier Transform (FFT) . The frequency domain signal includes a separate OFDM symbol stream for each subcarrier of the OFDM signal. The symbols on each subcarrier, and the reference signal, are recovered and demodulated by determining the most likely signal constellation points transmitted by the base station 310. These soft decisions may be based on channel estimates computed by the channel estimator 358. The soft decisions are then decoded and deinterleaved to recover the data and control signals that were originally transmitted by the base station 310 on the physical channel. The data and control signals are then provided to the controller/processor 359, which implements layer 3 and layer 2 functionality.

The controller/processor 359 can be associated with a memory 360 that stores program codes and data. The memory 360 may be referred to as a computer-readable medium. In the UL, the controller/processor 359 provides demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, and control signal processing to recover IP packets from the EPC 160. The controller/processor 359 is also responsible for error detection using an ACK or NACK protocol to support HARQ operations.

Similar to the functionality described in connection with the DL transmission by the base station 310, the controller/processor 359 provides RRC layer functionality associated with system information (such as MIB, SIBs) acquisition, RRC connections, and measurement reporting; PDCP layer functionality associated with header compression /decompression, and security (ciphering, deciphering, integrity protection, integrity verification) ; RLC layer functionality associated with the transfer of upper layer PDUs, error correction through ARQ, concatenation, segmentation, and reassembly of RLC SDUs, re-segmentation of RLC data PDUs, and reordering of RLC data PDUs; and MAC layer functionality associated with mapping between logical channels and transport channels, multiplexing of MAC SDUs onto TBs, demultiplexing of MAC SDUs from TBs, scheduling information reporting, error correction through HARQ, priority handling, and logical channel prioritization.

Channel estimates derived by a channel estimator 358 from a reference signal or feedback transmitted by the base station 310 may be used by the TX processor 368 to select the appropriate coding and modulation schemes, and to facilitate spatial processing. The spatial streams generated by the TX processor 368 may be provided to different antenna 352 via separate transmitters 354TX. Each transmitter 354TX may modulate an RF carrier with a respective spatial stream for transmission.

The UL transmission is processed at the base station 310 in a manner similar to that described in connection with the receiver function at the UE 350. Each receiver 318RX receives a signal through its respective antenna 320. Each receiver 318RX recovers information modulated onto an RF carrier and provides the information to a RX processor 370.

The controller/processor 375 can be associated with a memory 376 that stores program codes and data. The memory 376 may be referred to as a computer-readable medium. In the UL, the controller/processor 375 provides demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, control signal processing to recover IP packets from the UE 350. IP packets from the controller/processor 375 may be provided to the EPC 160. The controller/processor 375 is also responsible for error detection using an ACK or NACK protocol to support HARQ operations. Information to be wirelessly communicated (such as for LTE or NR based communications) is encoded and mapped, at the PHY layer, to one or more wireless channels for transmission.

Figure 4 shows a sequence diagram illustrating an example message 400 exchange between a UE 402 and a number of

base stations

401 and 404–408. In some implementations, the UE 402 may be an example of the UE 104 or UE 350 of Figures 1 and 3, respectively. In some implementations, each of the

base stations

401 and 404–408 may be an example of the base station 102 or base station 310 of Figures 1 and 3, respectively. The base stations 404–408 may be any suitable base stations or nodes configured for improved RATs compared to the base station 401. For example, in some implementations, the base station 401 may be an eNB and the base stations 404–408 may be gNBs.

The UE 402 is initially connected to base station 401. While connected to base station 401, the UE 402 may detect or receive one or more SSBs (SSB1–SSB3) broadcast by one or more base stations in its vicinity during a cell search operation. As shown in Figure 4, the UE 402 may receive SSB1, SSB2, and SSB3 from the

base stations

404, 406, and 408. As described with respect to Figure 2B, each SSB may include a primary synchronization signal (PSS) , a secondary synchronization signal (SSS) , and a physical broadcast channel (PBCH) . The UE 402 may detect each SSB, for example, based on the presence of the PSS and the SSS. Further, the UE 402 may use the PSS and the SSS to decode the PBCH.

The UE 402 may then select one of the

base stations

404, 406, or 408 to register to based, at least in part, on a given selection criteria. In some aspects, the selection criteria may include a signal strength of the SSBs broadcast by each of the base stations 404–408. For example, the UE 402 may select a base station having the highest signal strength among the detected base stations 404–408 (while also exceeding a threshold signal strength) . More specifically, the UE 402 may measure the signal strength of a demodulation reference signal (DMRS) transmitted on the PBCH of each SSB broadcast by the base stations 404–408.

The UE 402 may not register to a base station associated with a TAC on the UE’s FTAC list. Thus, after selecting a base station, the UE 402 may determine whether the TAC associated with the selected base station is on the FTAC list. For example, the TAC may be included in the SSBs (or PBCH) broadcast by each of the base stations 404–408. In the example of Figure 4, the base station 404 is associated with a first TAC (TAC1) , the base station 406 is associated with a second TAC (TAC2) , and the base station 408 is associated with a third TAC (TAC3) .

In some implementations, the UE 402 may dynamically or iteratively select one or more base stations, during the cell selection operation, based on the TACs associated with each of the detected base stations 404–408. More specifically, the UE 402 may treat each of the detected base stations 404–408 as a candidate for selection until the base station is selected by the UE 402 or the UE 402 selects a base station having a TAC not associated with the FTAC list. For example, with each iteration of the cell selection operation, the UE 402 may select one of the detected base stations 404–408, based on the selection criteria, and remove the selected base station from a list of candidate base stations.

If the TAC associated with the selected base station is not on the FTAC list, the UE 402 may terminate the cell selection operation at the selected base station. If the TAC associated with the selected base station is on the FTAC list, the UE 402 may select a new base station (based on the selection criteria) from the remaining candidate base stations. For example, the UE 402 may select the base station having the next-highest signal strength among the remaining candidate base stations. The UE 402 may repeat this process until the UE 402 selects a base station associated with a TAC that is not on the FTAC list or the list of candidate base stations has been exhausted.

In the example of Figure 4, the UE 402 may determine SSB1 to have the highest signal strength among the received SSBs. Thus, the UE 402 may initially select the base station 404 in a first iteration of the cell selection operation. The UE 402 may further determine that TAC1 is associated with the FTAC list. As a result, the UE 402 may perform a second iteration of the cell selection operation. In the example of Figure 4, the UE 402 may select base station 406 in the second iteration of the cell selection operation. For example, the UE 402 may determine SSB2 to have the strongest, highest, or greatest signal strength among the received SSBs from the remaining

candidate base stations

406 and 408. The UE 402 may further determine that TAC2 is not associated with the FTAC list and subsequently terminate the cell selection operation.

After terminating the cell selection operation, the UE 402 may transmit a registration request to the selected base station 406. The base station 406 determines whether to accept or reject the UE 402, in response to the registration request, and transmits a registration response back to the UE 402 based on the determination. Although not shown, for simplicity, the base station 406 and the UE 402 may exchange additional messages (such as identity messages, authentication messages, or security messages) between the registration request and the registration response.

If the registration response indicates that the request has been accepted, the UE 402 may complete the registration procedure with the base station 406. However, if the registration response indicates that the request has been rejected (or the UE 402 does not receive a registration response from the base station 406) , the UE 402 may remain connected to base station 401 or attempt to register to another base station during a subsequent cell search or selection operation. In some aspects, the UE 402 may update its FTAC list based, at least in part, on the cause of the rejection. For example, the UE 402 may update the FTAC list to include TAC2 if the registration response indicates that the UE 402 is not allowed in the TA associated with the base station 406.

Figure 5 shows an illustrative flowchart depicting an example wireless communication operation 500. The example operation 500 may be performed by a wireless device such as any of the

UEs

104, 350, or 402 of Figures 1, 3, and 4, respectively.

The wireless device detects one or more SSBs broadcast by one or more base stations while connected to a current base station (502) . The wireless device selects a first base station of the one or more base stations based on a first selection criteria (504) . In some implementations, the first selection criteria may include a signal strength of each of the SSBs broadcast by the one or more base stations. In some implementations, the first selection criteria may determine that the SSBs broadcast by the first base station have greater signal strengths than the SSBs broadcast by other base stations of the one or more base stations. The wireless device further determines whether a TAC associated with the first base station is associated with an FTAC list (506) . The wireless device selectively transmits a registration request to a second base station of the one or more base stations based at least in part on the determination.

In some implementations, the wireless device may determine that the TAC associated with the first base station is not associated with the FTAC list. The wireless device may transmit the registration request to the first base station, in lieu of the second base station, responsive to determining that the TAC associated with the first base station is not associated with the FTAC list.

In some other implementations, the wireless device may determine that the TAC associated with the first base station is associated with the FTAC list. The wireless device may further select the second base station, based on the first selection criteria, among the one or more base stations not including the first base station. In selecting the second base station, the wireless device may determine that the SSBs broadcast by the second base station have greater signal strengths than the SSBs broadcast by other base stations of the one or more base stations not including the first base station. The wireless device may further determine that a TAC associated with the second base station is not associated with the FTAC list. The wireless device may transmit the registration request to the second base station, in lieu of the first base station, responsive to determining that the TAC associated with the second base station is not associated with the FTAC list.

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.

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 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.

Claims

A method of wireless communication, comprising:

detecting one or more synchronization signal blocks (SSBs) broadcast by one or more base stations while connected to a current base station;

selecting a first base station of the one or more base stations based on a first selection criteria;

determining whether a tracking area code (TAC) associated with the first base station is associated with a forbidden tracking area code (FTAC) list; and

selectively transmitting a registration request to a second base station of the one or more base stations based at least in part on the determination.
The method of claim 1, wherein the selecting comprises:

determining a signal strength of each SSB broadcast by the one or more base stations, the first selection criteria including the signal strengths of the SSBs.
The method of claim 2, wherein the selecting further comprises:

determining that the SSBs broadcast by the first base station have greater signal strengths than the SSBs broadcast by the second base station.
The method of claim 1, wherein the selectively transmitting comprises:

determining that the TAC associated with the first base station is not associated with the FTAC list; and

transmitting the registration request to the first base station in lieu of the second base station.
The method of claim 1, wherein the selectively transmitting comprises:

determining that the TAC associated with the first base station is associated with the FTAC list; and

selecting the second base station, based on the first selection criteria, among the one or more base stations not including the first base station.
The method of claim 5, wherein the selecting of the second base station comprises:

determining a signal strength of each SSB broadcast by the one or more base stations, the first selection criteria including the signal strengths of the SSBs; and

determining that the SSBs broadcast by the second base station have greater signal strengths than the SSBs broadcast by other base stations of the one or more base stations not including the first base station.
The method of claim 5, wherein the selectively transmitting comprises:

determining that a TAC associated with the second base station is not associated with the FTAC list; and

transmitting the registration request to the second base station in lieu of the first base station.
The method of claim 1, wherein the selectively transmitting comprises:

determining that the TAC associated with the first base station is associated with the FTAC list;

selecting the second base station, based on the first selection criteria, among the one or more base stations not including the first base station;

determining that a TAC associated with the second base station also is associated with the FTAC list; and

selecting a third base station, based on the first selection criteria, among the one or more base stations not including the first and second base stations.
The method of claim 8, wherein the selecting of the second base station comprises:

determining a signal strength of each SSB broadcast by the one or more base stations, the first selection criteria including the signal strengths of the SSBs; and

determining that the SSBs broadcast by the second base station have greater signal strengths than the SSBs broadcast by the third base station.
The method of claim 9, wherein the selecting of the third base station comprises:

determining that the SSBs broadcast by the third base station have greater signal strengths than the SSBs broadcast by other base stations of the one or more base stations not including the first and second base stations.
The method of claim 8, wherein the selectively transmitting comprises:

determining that a TAC associated with the third base station is not associated with the FTAC list; and

transmitting the registration request to the third base station in lieu of the first and second base stations.
A wireless communication device comprising:

at least one modem;

at least one processor communicatively coupled with the at least one modem; and

at least one memory communicatively coupled with the at least one processor and storing processor-readable code that, when executed by the at least one processor in conjunction with the at least one modem, causes the wireless communication device to perform the operations of claims 1–11.