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WO2021051336A1 - Évitement de transferts en alternance dans des réseaux cellulaires - Google Patents

Évitement de transferts en alternance dans des réseaux cellulaires Download PDF

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Publication number
WO2021051336A1
WO2021051336A1 PCT/CN2019/106613 CN2019106613W WO2021051336A1 WO 2021051336 A1 WO2021051336 A1 WO 2021051336A1 CN 2019106613 W CN2019106613 W CN 2019106613W WO 2021051336 A1 WO2021051336 A1 WO 2021051336A1
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Prior art keywords
handover
serving cell
cell
power
doubtful
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PCT/CN2019/106613
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English (en)
Inventor
Jianqiang Zhang
Jie Mao
Arvind Vardarajan Santhanam
Shashidhar Vummintala
Nanrun WU
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Qualcomm Inc
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Qualcomm Inc
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Priority to PCT/CN2019/106613 priority Critical patent/WO2021051336A1/fr
Publication of WO2021051336A1 publication Critical patent/WO2021051336A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W36/00—Hand-off or reselection arrangements
    • H04W36/0005—Control or signalling for completing the hand-off
    • H04W36/0055—Transmission or use of information for re-establishing the radio link
    • H04W36/0058—Transmission of hand-off measurement information, e.g. measurement reports

Definitions

  • Embodiments can provide and enable techniques for reducing or avoiding ping-pong handovers in cellular networks.
  • Wireless communication systems provide various telecommunication services such as telephony, video, data, messaging, and broadcasts. These 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 of an emerging telecommunication standard is the Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (E-UTRA) , commonly called Long-Term Evolution (LTE) .
  • LTE is a set of enhancements to the 3G UMTS mobile standard promulgated by the Third Generation Partnership Project (3GPP) . It is designed to better support mobile broadband Internet access by improving spectral efficiency, lower costs, improve services, make use of new spectrum, and better integrate with other open standards.
  • 3GPP Third Generation Partnership Project
  • a wireless user equipment can manage transmissions of measurement reports to reduce or avoid ping-pong handover scenarios.
  • a UE measures one or more characteristics of a channel, such as a reference signal received power (RSRP) , corresponding to a serving cell or a neighbor cell.
  • RSRP reference signal received power
  • the UE determines to forgo transmission of a measurement report based on the measurement, in order to avoid an unwanted handover from the serving cell to the neighbor cell.
  • a method of wireless communication operable at a user equipment (UE) served by a serving cell includes measuring one or more characteristics of a channel corresponding to at least one of the serving cell or a neighbor cell. The method further includes determining to forgo transmission of a measurement report based on the one or more characteristics of the channel, to avoid an unwanted handover from the serving cell to the neighbor cell.
  • UE user equipment
  • a UE served by a serving cell where the UE is configured for wireless communication.
  • the UE includes a processor, a transceiver communicatively coupled to the processor, and a memory communicatively coupled to the processor.
  • the processor and memory are configured to utilize the transceiver to measure one or more characteristics of a channel corresponding to at least one of the serving cell or a neighbor cell.
  • the processor and memory are further configured to determine to forgo transmission of a measurement report based on the one or more characteristics of the channel, to avoid an unwanted handover from the serving cell to the neighbor cell.
  • a UE served by a serving cell the UE configured for wireless communication.
  • the UE includes means for measuring one or more characteristics of a channel corresponding to at least one of the serving cell or a neighbor cell.
  • the UE further includes means for determining to forgo transmission of a measurement report based on the one or more characteristics of the channel, to avoid an unwanted handover from the serving cell to the neighbor cell.
  • a non-transitory computer readable medium storing processor-executable code.
  • the code includes instructions for causing a wireless UE served by a serving cell to measure one or more characteristics of a channel corresponding to at least one of the serving cell or a neighbor cell.
  • the code further includes instructions for causing the UE to determine to forgo transmission of a measurement report based on the one or more characteristics of the channel, to avoid an unwanted handover from the serving cell to the neighbor cell.
  • FIG. 1 is a diagram illustrating an example of a hardware implementation for an apparatus employing a processing system.
  • FIG. 2 is a diagram illustrating an example of a network architecture.
  • FIG. 3 is a diagram illustrating an example of an access network.
  • FIG. 4 is a diagram illustrating an example of a radio protocol architecture for the user and control plane.
  • FIG. 5 is a diagram illustrating an example of an evolved Node B and user equipment in an access network.
  • FIG. 6 is a chart illustrating an example of a ping-pong handover among two cells.
  • FIG. 7 is a chart illustrating an example of a ping-pong handover among four cells.
  • FIG. 8 is a flow chart illustrating a conventional process for user equipment measurement reporting and handovers.
  • FIG. 9 is a flow chart illustrating one example of doubtful handover logging according to an aspect of the disclosure.
  • FIG. 10 is a flow chart illustrating one example of unwanted handover management according to an aspect of the disclosure.
  • Implementations may range a spectrum from chip-level or modular components to non-modular, non-chip-level implementations and further to aggregate, distributed, or OEM devices or systems incorporating one or more aspects of the described innovations.
  • devices incorporating described aspects and features may also necessarily include additional components and features for implementation and practice of claimed and described embodiments.
  • transmission and reception of wireless signals necessarily includes a number of components for analog and digital purposes (e.g., hardware components including antenna, RF-chains, power amplifiers, modulators, buffer, processor (s) , interleaver, adders/summers, etc. ) .
  • innovations described herein may be practiced in a wide variety of devices, chip-level components, systems, distributed arrangements, end-user devices, etc. of varying sizes, shapes and constitution.
  • FIG. 1 is a conceptual diagram illustrating an example of a hardware implementation for an apparatus 100 employing a processing system 114.
  • a processing system 114 that includes one or more processors 104.
  • the apparatus 100 may be a user equipment (UE) as illustrated in any one or more of FIGs. 2, 3, and/or 5.
  • processors 104 include microprocessors, microcontrollers, digital signal processors (DSPs) , 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. That is, the processor 104, as utilized in an apparatus 100, may be used to implement any one or more of the processes described below and illustrated in FIGs. 8, 9, and/or 10.
  • the processing system 114 may be implemented with a bus architecture, represented generally by the bus 102.
  • the bus 102 may include any number of interconnecting buses and bridges depending on the specific application of the processing system 114 and the overall design constraints.
  • the bus 102 links together various circuits including one or more processors (represented generally by the processor 104) , a memory 105, and computer-readable media (represented generally by the computer-readable medium 106) .
  • the bus 102 may also link various other circuits such as timing sources, peripherals, voltage regulators, and power management circuits, which are well known in the art, and therefore, will not be described any further.
  • a bus interface 108 provides an interface between the bus 102 and a transceiver 110.
  • the transceiver 110 provides a means for communicating with various other apparatus over a transmission medium.
  • a user interface 112 e.g., keypad, display, speaker, microphone, joystick
  • the processor 104 is responsible for managing the bus 102 and general processing, including the execution of software stored on the computer-readable medium 106.
  • the software when executed by the processor 104, causes the processing system 114 to perform the various functions described below for any particular apparatus.
  • the computer-readable medium 106 may also be used for storing data that is manipulated by the processor 104 when executing software.
  • Software shall be construed broadly to mean instructions, instruction sets, code, code segments, program code, programs, subprograms, software modules, 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.
  • the software may reside on a computer-readable medium 106.
  • the computer-readable medium 106 may be a non-transitory computer-readable medium.
  • a non-transitory computer-readable medium include, by way of example, a magnetic storage device (e.g., hard disk, floppy disk, magnetic strip) , an optical disk (e.g., compact disk (CD) , digital versatile disk (DVD) ) , a smart card, a flash memory device (e.g., card, stick, key drive) , random access memory (RAM) , read only memory (ROM) , programmable ROM (PROM) , erasable PROM (EPROM) , electrically erasable PROM (EEPROM) , a register, a removable disk, and any other suitable medium for storing software and/or instructions that may be accessed and read by a computer.
  • a magnetic storage device e.g., hard disk, floppy disk, magnetic strip
  • an optical disk e.g., compact disk (CD) , digital versatile disk (DVD)
  • the computer-readable medium 106 may be resident in the processing system 114, external to the processing system 114, or distributed across multiple entities including the processing system 114.
  • the computer-readable medium 106 may be embodied in a computer-program product.
  • a computer-program product may include a computer-readable medium in packaging materials.
  • FIG. 2 is a diagram illustrating an LTE network architecture 200 employing various apparatuses 100 (See FIG. 1) .
  • the LTE network architecture 200 may be referred to as an Evolved Packet System (EPS) 200.
  • the EPS 200 may include one or more user equipment (UE) 202, an Evolved UMTS Terrestrial Radio Access Network (E-UTRAN) 204, an Evolved Packet Core (EPC) 210, a Home Subscriber Server (HSS) 220, and an Operator’s IP Services 222.
  • the EPS can interconnect with other access networks, but for simplicity those entities/interfaces are not shown.
  • the EPS provides packet-switched services, however, as those skilled in the art will readily appreciate, the various concepts presented throughout this disclosure may be extended to networks providing circuit-switched services.
  • the E-UTRAN includes the evolved Node B (eNB) 206 and other eNBs 208.
  • the eNB 206 provides user and control plane protocol terminations toward the UE 202.
  • the eNB 206 may be connected to the other eNBs 208 via an X2 interface (i.e., backhaul) .
  • the eNB 206 may also be referred to by those skilled in the art as a base station, a base transceiver station, a radio base station, a radio transceiver, a transceiver function, a basic service set (BSS) , an extended service set (ESS) , or some other suitable terminology.
  • the eNB 206 provides an access point to the EPC 210 for a UE 202.
  • Examples of UEs 202 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 (e.g., MP3 player) , a camera, a game console, or any other similar functioning device.
  • SIP session initiation protocol
  • PDA personal digital assistant
  • the UE 202 may also be referred to by those skilled in the art as 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.
  • the eNB 206 is connected by an S1 interface to the EPC 210.
  • the EPC 210 includes a Mobility Management Entity (MME) 212, other MMEs 214, a Serving Gateway 216, and a Packet Data Network (PDN) Gateway 218.
  • MME Mobility Management Entity
  • PDN Packet Data Network
  • the MME 212 is the control node that processes the signaling between the UE 202 and the EPC 210.
  • the MME 212 provides bearer and connection management. All user IP packets are transferred through the Serving Gateway 216, which itself is connected to the PDN Gateway 218.
  • the PDN Gateway 218 provides UE IP address allocation as well as other functions.
  • the PDN Gateway 218 is connected to the Operator’s IP Services 222.
  • the Operator’s IP Services 222 include the Internet, the Intranet, an IP Multimedia Subsystem (IMS) , and a PS Streaming Service (PSS) .
  • IMS IP Multimedia Subsystem
  • FIG. 3 is a diagram illustrating an example of an access network in an LTE network architecture.
  • the access network 300 is divided into a number of cellular regions (cells) 302.
  • One or more lower power class eNBs 308, 312 may have cellular regions 310, 314, respectively, that overlap with one or more of the cells 302.
  • the lower power class eNBs 308, 312 may be femto cells (e.g., home eNBs (HeNBs) ) , pico cells, or micro cells.
  • HeNBs home eNBs
  • a higher power class or macro eNB 304 is assigned to a cell 302 and is configured to provide an access point to the EPC 210 for all the UEs 306 in the cell 302.
  • the eNB 304 is responsible for all radio related functions including radio bearer control, admission control, mobility control, scheduling, security, and connectivity to the serving gateway 216 (see FIG. 2) .
  • the modulation and multiple access scheme employed by the access network 300 may vary depending on the particular telecommunications standard being deployed.
  • OFDM is used on the DL
  • SC-FDMA is used on the UL to support both frequency division duplexing (FDD) and time division duplexing (TDD) .
  • FDD frequency division duplexing
  • TDD time division duplexing
  • the various concepts presented herein are well suited for LTE applications. However, these concepts may be readily extended to other telecommunication standards employing other modulation and multiple access techniques. By way of example, these concepts may be extended to Evolution-Data Optimized (EV-DO) or Ultra Mobile Broadband (UMB) .
  • EV-DO Evolution-Data Optimized
  • UMB Ultra Mobile Broadband
  • EV-DO and UMB are air interface standards promulgated by the 3rd Generation Partnership Project 2 (3GPP2) as part of the CDMA2000 family of standards and employs CDMA to provide broadband Internet access to mobile stations. These concepts may also be extended to Universal Terrestrial Radio Access (UTRA) employing Wideband-CDMA (W-CDMA) and other variants of CDMA, such as TD-SCDMA; Global System for Mobile Communications (GSM) employing TDMA; and Evolved UTRA (E-UTRA) , Ultra Mobile Broadband (UMB) , IEEE 802.11 (Wi-Fi) , IEEE 802.16 (WiMAX) , IEEE 802.20, and Flash-OFDM employing OFDMA.
  • UMB Ultra Mobile Broadband
  • IEEE 802.11 Wi-Fi
  • WiMAX IEEE 802.16
  • IEEE 802.20 Flash-OFDM employing OFDMA.
  • UTRA, E-UTRA, UMTS, LTE and GSM are described in documents from the 3GPP organization.
  • CDMA2000 and UMB are described in documents from the 3GPP2 organization.
  • the actual wireless communication standard and the multiple access technology employed will depend on the specific application and the overall design constraints imposed on the system.
  • the radio protocol architecture may take on various forms depending on the particular application.
  • An example for an LTE system will now be presented with reference to FIG. 4.
  • FIG. 4 is a conceptual diagram illustrating an example of the radio protocol architecture for the user and control planes.
  • Layer 1 is the lowest layer and implements various physical layer signal processing functions. Layer 1 will be referred to herein as the physical layer 406.
  • Layer 2 (L2 layer) 408 is above the physical layer 406 and is responsible for the link between the UE and eNB over the physical layer 406.
  • the L2 layer 408 includes a media access control (MAC) sublayer 410, a radio link control (RLC) sublayer 412, and a packet data convergence protocol (PDCP) 414 sublayer, which are terminated at the eNB on the network side.
  • MAC media access control
  • RLC radio link control
  • PDCP packet data convergence protocol
  • the UE may have several upper layers above the L2 layer 408 including a network layer (e.g., IP layer) that is terminated at the PDN gateway 218 (see FIG. 2) on the network side, and an application layer that is terminated at the other end of the connection (e.g., far end UE, server, etc. ) .
  • IP layer e.g., IP layer
  • the PDCP sublayer 414 provides multiplexing between different radio bearers and logical channels.
  • the PDCP sublayer 414 also provides header compression for upper layer data packets to reduce radio transmission overhead, security by ciphering the data packets, and handover support for UEs between eNBs.
  • the RLC sublayer 412 provides segmentation and reassembly of upper layer data packets, retransmission of lost data packets, and reordering of data packets to compensate for out-of-order reception due to hybrid automatic repeat request (HARQ) .
  • the MAC sublayer 410 provides multiplexing between logical and transport channels.
  • the MAC sublayer 410 is also responsible for allocating the various radio resources (e.g., resource blocks) in one cell among the UEs.
  • the MAC sublayer 410 is also responsible for HARQ operations.
  • the radio protocol architecture for the UE and eNB is substantially the same for the physical layer 406 and the L2 layer 408 with the exception that there is no header compression function for the control plane.
  • the control plane also includes a radio resource control (RRC) sublayer 416 in Layer 3.
  • RRC sublayer 416 is responsible for obtaining radio resources (i.e., radio bearers) and for configuring the lower layers using RRC signaling between the eNB and the UE.
  • FIG. 5 is a block diagram of an eNB 510 in communication with a UE 550 in an access network.
  • a controller/processor 575 implements the functionality of the L2 layer described earlier in connection with FIG. 4.
  • the controller/processor 575 provides header compression, ciphering, packet segmentation and reordering, multiplexing between logical and transport channels, and radio resource allocations to the UE 550 based on various priority metrics.
  • the controller/processor 575 is also responsible for HARQ operations, retransmission of lost packets, and signaling to the UE 550.
  • the TX processor 516 implements various signal processing functions for the L1 layer (i.e., physical layer) .
  • the signal processing functions includes coding and interleaving to facilitate forward error correction (FEC) at the UE 550 and mapping to signal constellations based on various modulation schemes (e.g., binary phase-shift keying (BPSK) , quadrature phase-shift keying (QPSK) , M-phase-shift keying (M-PSK) , M-quadrature amplitude modulation (M-QAM) ) .
  • FEC forward error correction
  • BPSK binary phase-shift keying
  • QPSK quadrature phase-shift keying
  • M-PSK M-phase-shift keying
  • M-QAM M-quadrature amplitude modulation
  • Each stream is then mapped to an OFDM subcarrier, multiplexed with a reference signal (e.g., pilot) in the time and/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 precoded to produce multiple spatial streams.
  • Channel estimates from a channel estimator 574 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 and/or channel condition feedback transmitted by the UE 550.
  • Each spatial stream is then provided to a different antenna 520 via a separate transmitter 518TX.
  • Each transmitter 518TX modulates an RF carrier with a respective spatial stream for transmission.
  • each receiver 554RX receives a signal through its respective antenna 552.
  • Each receiver 554RX recovers information modulated onto an RF carrier and provides the information to the receiver (RX) processor 556.
  • the RX processor 556 implements various signal processing functions of the L1 layer.
  • the RX processor 556 performs spatial processing on the information to recover any spatial streams destined for the UE 550. If multiple spatial streams are destined for the UE 550, they may be combined by the RX processor 556 into a single OFDM symbol stream.
  • the RX processor 556 then converts the OFDM symbol stream from the time-domain to the frequency domain using a Fast Fourier Transform (FFT) .
  • FFT Fast Fourier Transform
  • the frequency domain signal comprises a separate OFDM symbol stream for each subcarrier of the OFDM signal.
  • the symbols on each subcarrier, and the reference signal is recovered and demodulated by determining the most likely signal constellation points transmitted by the eNB 510.
  • These soft decisions may be based on channel estimates computed by the channel estimator 558.
  • the soft decisions are then decoded and deinterleaved to recover the data and control signals that were originally transmitted by the eNB 510 on the physical channel.
  • the data and control signals are then provided to the controller/processor 559.
  • the processing system 114 described in relation to FIG. 1 includes the UE 550.
  • the processing system 114 includes the TX processor 568, the RX processor 556, and the controller/processor 559.
  • the controller/processor 559 implements the L2 layer described earlier in connection with FIG. 4.
  • the control/processor 559 provides demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, control signal processing to recover upper layer packets from the core network.
  • the upper layer packets are then provided to a data sink 562, which represents all the protocol layers above the L2 layer.
  • Various control signals may also be provided to the data sink 562 for L3 processing.
  • the controller/processor 559 is also responsible for error detection using an acknowledgement (ACK) and/or negative acknowledgement (NACK) protocol to support HARQ operations.
  • ACK acknowledgement
  • NACK negative acknowledgement
  • a data source 567 is used to provide upper layer packets to the controller/processor 559.
  • the data source 567 represents all protocol layers above the L2 layer (L2) .
  • the controller/processor 559 implements the L2 layer for the user plane and the control plane by providing header compression, ciphering, packet segmentation and reordering, and multiplexing between logical and transport channels based on radio resource allocations by the eNB 510.
  • the controller/processor 559 is also responsible for HARQ operations, retransmission of lost packets, and signaling to the eNB 510.
  • Channel estimates derived by a channel estimator 558 from a reference signal or feedback transmitted by the eNB 510 may be used by the TX processor 568 to select the appropriate coding and modulation schemes, and to facilitate spatial processing.
  • the spatial streams generated by the TX processor 568 are provided to different antenna 552 via separate transmitters 554TX. Each transmitter 554TX modulates an RF carrier with a respective spatial stream for transmission.
  • the UL transmission is processed at the eNB 510 in a manner similar to that described in connection with the receiver function at the UE 550.
  • Each receiver 518RX receives a signal through its respective antenna 520.
  • Each receiver 518RX recovers information modulated onto an RF carrier and provides the information to a RX processor 570.
  • the RX processor 570 implements the L1 layer.
  • the controller/processor 559 implements the L2 layer described earlier in connection with FIG. 6.
  • the control/processor 559 provides demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, control signal processing to recover upper layer packets from the UE 550.
  • Upper layer packets from the controller/processor 575 may be provided to the core network.
  • the controller/processor 559 is also responsible for error detection using an ACK and/or NACK protocol to support HARQ operations.
  • a UE In an LTE network, based on parameters it receives from the network, a UE performs various channel measurements and sends measurement reports to the RAN. These measurements include determination of a Reference Signal Received Power (RSRP) and/or reference signal received quality (RSRQ) of the UE's serving cell or serving cells, an RSRP/RSRQ of one or more other listed cells, and may include an RSRP/RSRQ of other detected cells not listed by the RAN but detected by the UE.
  • RSRP Reference Signal Received Power
  • RSRQ reference signal received quality
  • the UE may make measurements of other properties of a channel, and further, a UE’s transmission of a measurement report may be triggered based on other quantities or properties in addition to or in the alternative to the RSRP and RSRQ.
  • Measurement reports may include information for LTE base stations (eNBs) , other (non-LTE) RATs, and transmission resource pools for sidelink communication. Transmission of these measurement reports is triggered upon satisfaction of certain reporting criteria. Some of these measurement reports, and their reporting criteria, are summarized in the list below. Other measurement reports not listed below are also used in LTE specifications. In addition, the various aspects of this disclosure are not limited to these specific listed measurement reports.
  • Event A1-Serving Cell becomes better than a Threshold. If the measurement result of the serving cell is greater than the threshold parameter configured for Event A1, the UE transmits a measurement report indicating Event A1.
  • a hysteresis parameter is used to reduce ping-ponging into and out of this event.
  • Event A2-Serving Cell becomes worse than a Threshold. If the measurement result of the serving cell is less than the threshold parameter configured for Event A2, the UE transmits a measurement report indicating Event A2.
  • a hysteresis parameter is used to reduce ping-ponging into and out of this event.
  • Event A3-Neighbor Cell becomes better than Serving Cell. If the measurement result of a neighboring cell is greater than the measurement result of the serving cell, the UE transmits a measurement report indicating Event A3.
  • a hysteresis parameter is used to reduce ping-ponging into and out of this event.
  • Event A4-Neighbor Cell becomes better than a Threshold. If the measurement result of a neighboring cell is greater than the threshold parameter configured for Event A4, the UE transmits a measurement report indicating Event A4. A hysteresis parameter is used to reduce ping-ponging into and out of this event.
  • Event A5-Serving Cell becomes worse than Threshold-1, and Neighbor Cell becomes better than Threshold-2. If the measurement result of the serving cell is less than the first threshold parameter (Thresh1) configured for Event A5, and in addition, the measurement result of a neighbor cell becomes greater than the second threshold parameter (Thresh2) configured for Event A5, the UE transmits a measurement report indicating Event A5.
  • a hysteresis parameter is used to reduce ping-ponging into and out of this event.
  • the RAN In response to a UE's transmission of a measurement report, including but not limited to those listed above, the RAN (e.g., an eNB, the UE's serving cell, or any suitable node in the RAN) may determine to initiate a handover for the UE. In this fashion, by taking a UE's channel measurements into account, the RAN can dynamically maintain good channel quality for UEs by ensuring such UEs are always served by the best cell.
  • the RAN e.g., an eNB, the UE's serving cell, or any suitable node in the RAN
  • one or more network-configured parameters that the UE uses to determine when to transmit measurement reports may be misconfigured.
  • a UE may transmit a measurement report even if a neighbor cell has a lower RSRP than its serving cell.
  • This sort of misconfiguration may simply be caused by mistake; the inventors have noticed that such mistakes occur in real-world networks with sufficient regularity to noticeably impact user experience.
  • the RAN may hand over the UE from a strong cell to a weak cell. Once this occurs, based on subsequent measurement reporting, the RAN may quickly hand over the UE back to the previous serving cell. If the abnormal decision-making condition persists, the UE might suffer from a ping-pong handover between 2 cells, or among 3 or more cells. This ping-pong handover issue can cause a poor user experience, including but not limited to increased power consumption or a dropped connection.
  • the eNB After each handover, a small amount of data is transmitted over the air. For example, in an LTE network the eNB transmits a PDCP status report as a part of a PDCP reestablishment procedure, which resets an inactivity timer at the eNB.
  • the inactivity timer In a ping-pong handover scenario, within few seconds, another handover takes place. Therefore, at the eNB, the inactivity timer never expires.
  • the RAN never releases the UE, and the UE remains in connected mode and cannot go to idle mode.
  • the UE can continue performing such a ping-pong handover indefinitely, without ever entering into idle mode. This circumstance can cause a dramatic increase in the power consumption at the UE.
  • the UE might drop the connection if a handover failure occurs.
  • a ping-pong handover scenario can occur when a UE is served by a relatively weak cell. That is, the UE is served by a cell with signal strength very close to the signal strength of a neighbor cell.
  • FIG. 6 two charts illustrate this problem case.
  • the line shows the UE ping-ponging between Cell A and Cell B.
  • the RSRP measured by the UE for Cells A and B remains relatively constant, with Cell A approximately –100 dBm, and Cell B approximately –90 dBm.
  • the threshold parameter configured for Event A4 is equivalent to an RSRP of –106dBm.
  • the network configures Event A4 for Cell A, which is now a neighbor cell.
  • the threshold parameter configured for Event A4 is equivalent to an RSRP of –105dBm.
  • a measurement result of the neighbor cell now Cell A
  • RSRP –100dBm
  • the UE transmits a measurement report indicating Event A4.
  • the network carries out a handover for the UE from Cell B back to Cell A. This process repeats indefinitely, and manifests as a ping-pong handover.
  • a ping-pong handover scenario among multiple cells can occur when a UE is misconfigured, or given an improper threshold parameter for Event A4.
  • FIG. 7 two charts illustrate this problem case.
  • the line shows the UE undergoing ping-pong handovers among Cells A–D.
  • the RSRP measured by the UE for Cells A–D remains relatively constant, with Cell A approximately –100dBm, Cell B approximately –105dBm, Cell C approximately –95dBm, and Cell D approximately –85dBm.
  • the threshold parameter configured for Event A4 for the UE is equivalent to an RSRP of –106dBm.
  • Cell D always has the highest RSRP as measured by the UE.
  • the network repeatedly hands over the UE from this high-power cell to a lower-power cell, as indicated by the arrows in FIG. 7.
  • four unwanted handovers 702 from Cell D to Cell A are illustrated with black arrows.
  • the network carries out a handover for the UE from Cell D to Cell A.
  • one unwanted handover 706 from cell D to Cell B is illustrated with a white arrow.
  • the UE When the UE is served by any of Cells A, B, or C, there is always a stronger neighbor cell than the respective serving cell. That is, as illustrated in FIG. 7, if the UE is served by Cell C, Cell D is stronger; if the UE is served by Cell A, both Cells C and D are stronger; and if the UE is served by Cell B, Cells A, C, and D are all stronger than the serving cell. Therefore, whenever the UE is served by any of cells A, B, or C, the UE may transmit a measurement report indicating Event A3, to inform the RAN that the measurement result of a neighboring cell is greater than the measurement result of the serving cell. In this event, the RAN may hand over the UE from the serving cell to the reported neighbor cell. As seen in FIG. 7, whenever these Event A3 handovers eventually send the UE to the strongest cell, Cell D, because of the misconfigured threshold parameter for Event A4, the ping-pong handover scenario continues. This misconfiguration can continue indefinitely.
  • a ping-pong handover scenario between two cells can occur when the first threshold parameter (Thresh1) for Event A5 is misconfigured to a value that is too high. For example, assume that a UE is at a location proximate to Cells A and B, such that the UE measures an RSRP for Cell A of –93dBm, and an RSRP for Cell B of –100dBm. That is, Cell A is the stronger cell at the UE's current location.
  • the first threshold parameter (Thresh1) for Event A5 is configured for –90dBm
  • the second threshold parameter (Thresh2) for Event A5 is configured for –107dBm.
  • configuration of the first threshold parameter Thresh1 as –90dBm represents a misconfiguration for this parameter, as a more suitable value for Thresh1 may be lower than –110dBm.
  • the RSRP for the serving cell which as previously described is –93dBm, is lower than the first threshold parameter Thresh1.
  • the RSRP for the neighbor cell, Cell B at –100dBm, is greater than the second threshold parameter Thresh2. Therefore, the UE transmits a measurement report indicating Event A5, and the network hands over the UE to Cell B.
  • the UE measures the RSRP for the neighbor cell, Cell A, at –93dBm. Because this value is greater than the RSRP for the serving cell, Cell A (–100 dBm) , the UE transmits a measurement report indicating Event A3, and the network hands over the UE to Cell A. If the UE, when it is served by Cell A, continues to receive the misconfigured Thresh1 value for Event A5 from the RAN, then this ping-pong handover scenario may continue indefinitely.
  • a doubtful handover may be defined as a handover that the RAN triggers for a UE from its serving cell to a target cell, when the UE's latest measurement of its serving cell's RSRP is higher than its latest measurement of the target cell.
  • a doubtful handover corresponds to a handover from a strong cell to a weak cell.
  • such doubtful handovers may be limited only to intra-RAN handovers. That is, a UE may omit from its list of such doubtful handovers any handovers triggered from a serving cell to a neighbor cell in a different RAN.
  • Handover is an intra-RAT handover (optional) .
  • the UE may store in memory information relating to the doubtful handover.
  • This information may include an identifier of the source cell: for example, a global cell ID of the source cell.
  • This information may further include an identifier of the target cell: for example, in an LTE network, an E-UTRA Absolute Radio Frequency Channel Number (EARFCN) and/or a Physical Cell Identifier (PCI) of the target cell.
  • this information may include a timestamp indicating the time of the doubtful handover.
  • the Doubtful Handover Table above shows an example of a structure that a UE may utilize for logging or storing its doubtful handover history.
  • a UE may structure a doubtful handover table as follows in its memory.
  • a UE may utilize such a table including several (e.g., 10) information lines, where each information line includes the following 5 elements:
  • the UE may initialize each element of this table to a value of 0. Updates to the table are described below.
  • an unwanted handover may be a handover that is likely to be part of a ping-pong handover scenario, or a handover loop.
  • an unwanted handover may be defined as a condition where a UE is triggered to perform the same doubtful handover greater than a threshold number of times (M times) within a given time span (N seconds) .
  • M times a threshold number of times
  • N seconds a given time span
  • any suitable threshold number of times M, and any suitable time span N may be utilized within the scope of this disclosure to identify unwanted handovers.
  • M 3
  • N 60 seconds
  • the unwanted handover condition or state may be time-limited (e.g., E minutes) . That is, once the conditions defined above for an unwanted handover are satisfied, an unwanted handover state timer may begin.
  • a UE may utilize the above doubtful handover table in the following manner to determine whether an unwanted handover state exists.
  • the UE may determine whether the handover corresponds to a doubtful handover.
  • the UE may perform the following steps to update the doubtful handover table and log the doubtful handover, regardless of the future success or failure of the handover itself.
  • the UE may count the number of information lines in the doubtful handover table that satisfy all the following conditions.
  • the UE uses this number of information lines that satisfy all conditions as a parameter K.
  • the EARFCN of the target cell matches target_EARFCN field
  • the UE may insert a new line in the doubtful handover table.
  • the parameter K ⁇ M –1 i.e., the counted number of lines in the doubtful handover table that meet the above conditions is greater than or equal to one less than the threshold number M of doubtful handovers
  • the UE may insert a new information line into the doubtful handover table, including the 5 fields below:
  • the UE may insert a new information line into the doubtful handover table, including the 5 fields below:
  • the UE may then continue with conventional operations, such as carrying out the triggered handover to the identified neighbor cell.
  • the UE may omit transmission of a measurement report if an unwanted handover state exists. For example, as described above, based on satisfaction of certain criteria such as a series of doubtful handovers taking place within a given time span, a UE may enter an unwanted handover state.
  • the UE may create a timer associated with the unwanted handover state such that the unwanted handover state persists for a suitable length of time. For example, an unwanted handover state timer may persist for 20 minutes, or any other suitable length of time.
  • the UE may determine whether an unwanted handover state exists. For example, the unwanted handover state may persist for a suitable period, e.g., for 20 minutes after entry into an unwanted handover state. If the unwanted handover state currently exists, a UE may determine to forgo transmitting a measurement report, even though the specified conditions for transmission of the measurement report exist. That is, a UE may add one or more conditions to those identified in its operational specifications, which should be satisfied prior to transmitting a measurement report.
  • a UE may forgo transmission of a measurement report when the combination of source cell and target cell match those of an unwanted handover, and if the UE's serving cell RSRP measurement is greater than or equal to the target cell's RSRP measurement.
  • the UE may revert to conventional operation. That is, the UE may continue transmitting measurement reports according to the usual conditions, and logging doubtful handovers as described above until such a time as another unwanted handover state may come to exist.
  • the unwanted handover state may apply only to a subset of all possible measurement report transmissions.
  • forgoing to transmit a measurement report may apply only to Event A4-and Event A5-triggered measurement reports.
  • a UE may utilize the doubtful handover table shown and described above as follows to determine how to handle a measurement report. That is, when UE makes a channel measurement, if the channel measurement would trigger a measurement report according to conventional operations, the UE may check whether there is an information line in the doubtful handover table that satisfies all 3 conditions below.
  • the UE may further check the following 3 conditions:
  • ⁇ Condition 5 the latest measurement of the neighbor cell's reference signal received quality (RSRQ) is lower than the latest measurement of UE's serving cell's RSRQ
  • the UE may forgo transmission of the corresponding measurement report.
  • a network e.g., RAN
  • a UE may measure one or more characteristics (e.g., a power) of a set of one or more inter/intra-frequency neighbor cells.
  • the UE may then determine whether to generate and transmit a measurement report. Here, if the UE determines to forgo transmission of a measurement report, the following steps will not take place. However, if the UE determines to transmit the measurement report, then, upon reception of a measurement report, the network decides whether a handover is needed. If a handover is needed, the network sends a handover instruction to the UE, and in response, the UE executes a handover. If a UE detects a ping-pong handover is occurring, then the UE may take the initiative to discard some measurement reports, as described above.
  • the bandwidth of any given cell can vary.
  • the bandwidth of the serving cell and target cell were not considered. Therefore, according to a further aspect of the disclosure, a UE may additionally take the bandwidth of a serving cell and/or neighbor cell into consideration when determining how to handle transmission of a measurement report. That is, in an aspect of the disclosure, the definition of a doubtful handover can be modified to include considerations of the respective cells'bandwidths.
  • a modified definition of a doubtful handover may be as follows.
  • the UE may call the handover a doubtful handover if its latest measurement of its serving cell’s RSRP, plus an offset ⁇ , is greater than the UE’s latest measurement of the target cell’s RSRP.
  • ⁇ represents an offset for the serving cell, and may be given in terms of dB.
  • the value of ⁇ can be determined as a function of the serving cell bandwidth, the neighbor/target cell bandwidth.
  • the offset parameter ⁇ may be set to 0 when the serving cell's RSRP is not greater than a suitable RSRP threshold value Th_SrvRsrp. That is, if the serving cell's latest RSRP measurement is greater than an RSRP threshold Th_SrvRsrp, then the offset ⁇ may be set to a non-zero value; otherwise, it may be set to 0. For example, when the UE's serving cell has the same bandwidth as the target cell, the UE may set the value for the offset parameter ⁇ to zero or, in some examples, a small hysteresis value.
  • a UE's serving cell has a 20MHz bandwidth
  • a target cell has a 10 MHz bandwidth.
  • the UE's serving cell has lower bandwidth than the target cell, then a handover to a target cell with slightly lower RSRP than the UE's serving cell might be acceptable. In such a case, the UE may set the value of the offset parameter ⁇ to a negative value. On the other hand, if the UE's serving cell has higher bandwidth than the target cell, then the UE might set the value of the offset parameter ⁇ to discourage a handover to that target cell. In such a case, the UE may set the value of the offset parameter ⁇ to a positive value.
  • the offset ⁇ can be a function of one or more additional variables including the serving cell's RSRP/RSRQ. For example, if a serving cell's measured RSRP is higher than a suitable RSRP threshold value Th_SrvRsrp, then the offset parameter ⁇ may be determined as a function of the serving cell bandwidth, the target cell bandwidth, and the serving cell’s RSRP/RSRQ. That is, a UE may focus on how to choose a better cell, rather than how to survive a potential loss of service. On the other hand, when the offset parameter ⁇ is set to zero 0, the UE focuses on how to survive a potential loss of service, rather than how to choose a better cell.
  • a UE may use a look-up table to determine the value of the offset parameter ⁇ and the RSRP threshold value Th_SrvRsrp.
  • the table below provides one non-limiting example of such a look-up table that a UE may utilize according to one aspect of this disclosure.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Mobile Radio Communication Systems (AREA)

Abstract

L'invention concerne un procédé, un appareil et un produit programme d'ordinateur pour une communication sans fil dans lesquels un équipement utilisateur (UE) peut gérer des transmissions de rapports de mesure pour réduire ou éviter des scénarios de transfert en alternance. Dans un exemple, un UE mesure une ou plusieurs caractéristiques d'un canal, tel qu'une puissance reçue de signal de référence (RSRP), correspondant à une cellule de desserte ou à une cellule voisine. L'UE détermine la transmission d'un rapport de mesure sur la base de la mesure afin d'éviter un transfert indésirable de la cellule de desserte à la cellule voisine.
PCT/CN2019/106613 2019-09-19 2019-09-19 Évitement de transferts en alternance dans des réseaux cellulaires Ceased WO2021051336A1 (fr)

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