HK1155312A1 - Optimized serving dual cell change - Google Patents

Optimized serving dual cell change

Info

Publication number
HK1155312A1
HK1155312A1 HK11109506.5A HK11109506A HK1155312A1 HK 1155312 A1 HK1155312 A1 HK 1155312A1 HK 11109506 A HK11109506 A HK 11109506A HK 1155312 A1 HK1155312 A1 HK 1155312A1
Authority
HK
Hong Kong
Prior art keywords
cell change
dual cell
serving dual
optimized
optimized serving
Prior art date
Application number
HK11109506.5A
Other languages
English (en)
Chinese (zh)
Inventor
‧帕尼
‧馬里內爾
‧佩爾蒂埃
Original Assignee
交互數字專利控股公司
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by 交互數字專利控股公司 filed Critical 交互數字專利控股公司
Publication of HK1155312A1 publication Critical patent/HK1155312A1/xx

Links

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W36/00—Hand-off or reselection arrangements
    • H04W36/24—Reselection being triggered by specific parameters
    • H04W36/26—Reselection being triggered by specific parameters by agreed or negotiated communication parameters
    • H04W36/28—Reselection being triggered by specific parameters by agreed or negotiated communication parameters involving a plurality of connections, e.g. multi-call or multi-bearer connections
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W36/00—Hand-off or reselection arrangements
    • H04W36/04—Reselecting a cell layer in multi-layered cells
    • 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
    • H04W36/0069—Transmission or use of information for re-establishing the radio link in case of dual connectivity, e.g. decoupled uplink/downlink
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W36/00—Hand-off or reselection arrangements
    • H04W36/08—Reselecting an access point
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W72/00—Local resource management
    • H04W72/04—Wireless resource allocation
    • H04W72/044—Wireless resource allocation based on the type of the allocated resource
    • H04W72/0453—Resources in frequency domain, e.g. a carrier in FDMA
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W72/00—Local resource management
    • H04W72/20—Control channels or signalling for resource management
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W88/00—Devices specially adapted for wireless communication networks, e.g. terminals, base stations or access point devices
    • H04W88/02—Terminal devices

Landscapes

  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Mobile Radio Communication Systems (AREA)
HK11109506.5A 2008-06-19 2011-09-08 Optimized serving dual cell change HK1155312A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US7400608P 2008-06-19 2008-06-19
PCT/US2009/047891 WO2009155480A1 (en) 2008-06-19 2009-06-19 Optimized serving dual cell change

Publications (1)

Publication Number Publication Date
HK1155312A1 true HK1155312A1 (en) 2012-05-11

Family

ID=41066099

Family Applications (1)

Application Number Title Priority Date Filing Date
HK11109506.5A HK1155312A1 (en) 2008-06-19 2011-09-08 Optimized serving dual cell change

Country Status (11)

Country Link
US (2) US9532288B2 (xx)
EP (3) EP2292044B1 (xx)
JP (3) JP5059971B2 (xx)
KR (4) KR20150060995A (xx)
CN (3) CN103997765B (xx)
AR (1) AR072195A1 (xx)
BR (1) BRPI0909948B1 (xx)
HK (1) HK1155312A1 (xx)
RU (1) RU2467513C2 (xx)
TW (3) TWM378576U (xx)
WO (1) WO2009155480A1 (xx)

Families Citing this family (78)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8687589B2 (en) * 2008-08-13 2014-04-01 Qualcomm Incorporated Neighbor cell search on a secondary carrier
US8369289B2 (en) * 2008-08-14 2013-02-05 Sony Mobile Communications Ab Reuse of training sequence between frequency-adjacent radio signals
KR101682034B1 (ko) 2008-08-18 2016-12-05 삼성전자주식회사 다중 밴드를 사용하는 광대역 무선통신 시스템에서 서브밴드의 선택적 사용을 위한 장치 및 방법
US9320039B2 (en) * 2008-10-31 2016-04-19 Unwired Planet, Llc Method and arrangement for user equipment switching between carriers in different frequency bands
EP2384052A1 (en) * 2009-01-16 2011-11-02 Sharp Kabushiki Kaisha Mobile station apparatus, base station apparatus, handoff method, and mobile communication system
CN101790200B (zh) 2009-01-23 2013-04-24 华为技术有限公司 上行载频管理方法、设备和系统
KR101652841B1 (ko) * 2009-02-02 2016-08-31 삼성전자 주식회사 반송파 결합을 지원하는 셀룰러 무선 통신시스템을 위한 라디오 링크 제어 방법 및 장치
WO2011100673A1 (en) * 2010-02-12 2011-08-18 Interdigital Patent Holdings, Inc. Method and apparatus for enhancing cell-edge user performance and signaling radio link failure conditions via downlink cooperative component carriers
US8774164B2 (en) * 2009-02-25 2014-07-08 At&T Mobility Ii Llc Adaptive R99 and HS PS (high speed packet-switched) link diversity for coverage and capacity enhancement of circuit-switched calls
US8989105B2 (en) 2009-03-17 2015-03-24 Htc Corporation Method of establishing multiple links with multiple component carriers and related communication device
US8989107B2 (en) * 2009-04-30 2015-03-24 Qualcomm Incorporated Activation deactivation of secondary UL carrier in DC HSUPA
BRPI1013144B1 (pt) * 2009-06-15 2021-03-02 Guangdong Oppo Mobile Telecommunications Corp., Ltd método e sistema para a operação de recepção descontínua para agregação de portadora avançada de evolução de longo prazo
WO2010146226A1 (en) * 2009-06-19 2010-12-23 Nokia Corporation Method and apparatus for managing carrier measurements
US8537778B1 (en) * 2009-06-25 2013-09-17 Sprint Spectrum L.P. Methods and systems for initiating a handoff based on EV-DO DRCLock
ES2360329B1 (es) * 2009-07-14 2012-05-08 Vodafone España, S.A.U. Método y controlador de red radio para seleccionar una tecnolog�?a de trasmisión para comunicaciones en redes móviles de �?rea amplia.
US8897258B2 (en) * 2009-07-15 2014-11-25 Electronics And Telecommunications Research Institute Method of transmitting data for reducing interference in hierarchical cell structure
US8942209B2 (en) * 2009-08-12 2015-01-27 Qualcomm Incorporated Systems and methods for supporting an enhanced serving cell change when moving among different cell types
EP2285159A1 (en) * 2009-08-13 2011-02-16 Alcatel Lucent Anchor carrier handover
CN101998615B (zh) * 2009-08-17 2014-06-11 中兴通讯股份有限公司 辅载波小区同步方法及终端
US8964536B2 (en) * 2009-10-05 2015-02-24 Qualcomm Incorporated Apparatus and method for dynamic load balancing in a multi-carrier wireless communication system
US8494453B2 (en) * 2009-11-03 2013-07-23 Htc Corporation Method of handling measurement and related communication device
CN102131244B (zh) * 2010-01-15 2016-01-20 中兴通讯股份有限公司 一种辅载波配对信息传递和获取的方法和系统
KR101607129B1 (ko) * 2010-01-28 2016-03-29 삼성전자주식회사 이동통신 시스템에서 핸드오버 결정 방법 및 장치
WO2011098308A1 (en) 2010-02-11 2011-08-18 Alcatel Lucent Inter-node b serving hs-dsch cell change with target cell pre-configuration and signaling of alternative configuration information to user equipment
JP5192503B2 (ja) * 2010-02-25 2013-05-08 株式会社エヌ・ティ・ティ・ドコモ 情報伝送方法、基地局装置及び移動局装置
JP5440248B2 (ja) 2010-02-25 2014-03-12 ソニー株式会社 ハンドオーバを制御するための方法、端末装置、基地局及び無線通信システム
EP2375850B1 (en) * 2010-04-06 2016-09-07 Alcatel Lucent Controlling communications in a multi-carrier wireless communication system
CN103338473B (zh) 2010-04-30 2016-04-06 华为技术有限公司 小区失效的处理设备
US8874117B2 (en) 2010-05-04 2014-10-28 Motorola Mobility Llc Handover during carrier aggregation operation in wireless communication network
US8891356B2 (en) 2010-06-28 2014-11-18 Qualcomm Incorporated System and method for multi-point HSDPA communication utilizing a multi-link RLC sublayer
US8989140B2 (en) * 2010-06-28 2015-03-24 Qualcomm Incorporated System and method for mobility in a multi-point HSDPA communication network
US8456989B1 (en) * 2010-06-30 2013-06-04 Sprint Spectrum L.P. Method and system for using supplemental channels for a communication session
US8675513B1 (en) 2010-06-30 2014-03-18 Sprint Spectrum L.P. Method and system for using multi-channel communication links
CN102378287B (zh) * 2010-08-11 2014-12-10 电信科学技术研究院 一种主小区更换的小区配置方法及装置
CN102083153B (zh) * 2010-08-12 2014-09-10 电信科学技术研究院 一种主小区更换的方法及装置
US9210624B2 (en) * 2010-08-17 2015-12-08 Google Technology Holdings LLC Method and apparatus for change of primary cell during carrier aggregation
US9191867B2 (en) * 2010-09-09 2015-11-17 Qualcomm Incorporated Dynamic switching between DC-HSDPA and SFDC-HSDPA
US8693437B2 (en) * 2010-09-14 2014-04-08 Htc Corporation Method of configuring secondary cells and related communication device
KR101797170B1 (ko) 2010-10-01 2017-11-15 인터디지탈 패튼 홀딩스, 인크 불연속 수신(drx)을 조정하는 방법
US10034205B2 (en) * 2010-10-01 2018-07-24 Telefonaktiebolaget Lm Ericsson (Publ) Positioning measurements and carrier switching in multi-carrier wireless communication networks
US8824307B2 (en) * 2010-10-13 2014-09-02 Qualcomm Incorporated Communicating between user equipment (UE) and independent serving sectors in a wireless communications system
US20120106511A1 (en) * 2010-11-03 2012-05-03 Chih-Hsiang Wu Method of Handling Primary Serving Cell Change
CN102469537A (zh) * 2010-11-03 2012-05-23 中兴通讯股份有限公司 Mimo系统中服务hs-dsch小区切换方法及系统
CN102083154A (zh) * 2010-11-05 2011-06-01 大唐移动通信设备有限公司 一种切换时辅小区配置的处理方法及其装置
US8989004B2 (en) 2010-11-08 2015-03-24 Qualcomm Incorporated System and method for multi-point HSDPA communication utilizing a multi-link PDCP sublayer
CN102325005B (zh) * 2011-07-18 2017-06-27 中兴通讯股份有限公司 一种终端对hs‑scch命令的实施方法、系统和终端
US9125098B2 (en) 2011-08-03 2015-09-01 Qualcomm Incorporated Method and apparatus for flow congestion control in multiflow networks
US8737211B2 (en) 2011-08-03 2014-05-27 Qualcomm Incorporated Methods and apparatuses for network configuration of user equipment communication modes in multiflow systems
EP2557843A1 (en) * 2011-08-12 2013-02-13 Alcatel Lucent Network node configuration
US9462512B2 (en) 2011-09-30 2016-10-04 Telefonaktiebolaget Lm Ericsson (Publ) Radio network controller, a user equipment, a radio network node and methods therein
CN103036637B (zh) * 2011-09-30 2017-04-12 中兴通讯股份有限公司 激活多流传输的ue发送hs‑dpcch的方法及ue
RU2601428C2 (ru) 2011-10-04 2016-11-10 Телефонактиеболагет Л М Эрикссон (Пабл) Способы и устройства для конфигурирования разнесения передачи восходящей линии связи во время изменения обслуживающей соты
GB2496204A (en) * 2011-11-07 2013-05-08 Renesas Mobile Corp Enabling mobility in a downlink packet access service
US9137717B2 (en) * 2012-01-13 2015-09-15 Qualcomm Incorporated Method and apparatus for managing mobility events in a dual-frequency dual-cell wireless communication network
US9320062B2 (en) * 2012-04-17 2016-04-19 Qualcomm Incorporated Communication in a heterogeneous network with carrier aggregation
WO2014017767A1 (ko) * 2012-07-23 2014-01-30 엘지전자 주식회사 반송파 집성 기법이 적용된 무선 통신 시스템에서 서빙 셀의 운용 방법 및 이를 위한 장치
US20140038605A1 (en) * 2012-07-31 2014-02-06 Firouz Behnamfar Devices and methods for cellular communication
CN104115523B (zh) * 2012-10-30 2018-10-09 华为技术有限公司 公共增强专用信道相对授权信道e-rgch信息交互方法、装置和系统
US9706451B2 (en) 2012-11-07 2017-07-11 Qualcomm Incorporated Method and apparatus for pre-configuring for a serving cell change to neighbor cells
WO2014071620A1 (zh) * 2012-11-09 2014-05-15 华为技术有限公司 一种上行更软切换的方法、用户设备和基站
WO2014090283A1 (en) * 2012-12-11 2014-06-19 Nokia Solutions And Networks Oy Liquid small cell radio link in dl for multiflow with hetnets
CN108200621B (zh) * 2012-12-28 2021-07-16 日本电气株式会社 无线电通信系统、无线电终端、通信控制方法和计算机可读介质
WO2014193354A1 (en) * 2013-05-29 2014-12-04 Intel Corporation Time-sliced wifi associations for make-before-break handover
WO2014190524A1 (zh) * 2013-05-30 2014-12-04 华为技术有限公司 一种切换小区的方法及装置
US20150038148A1 (en) * 2013-08-01 2015-02-05 Electronics And Telecommunications Research Institute Method and apparatus for handover based on cooperation between base stations
KR102236524B1 (ko) * 2013-09-27 2021-04-06 팬텍 주식회사 이중연결 방식을 이용하는 무선통신 시스템에서 서빙셀의 변경 방법 및 장치
KR102287928B1 (ko) 2013-09-27 2021-08-10 삼성전자 주식회사 이동 통신 시스템에서 복수의 캐리어를 이용하는 데이터 송수신 방법 및 장치
EP3120658B1 (en) * 2014-03-21 2018-06-20 Telefonaktiebolaget LM Ericsson (publ) Apparatus and methods for decoupling an uplink enhanced dedicated channel and high speed downlink shared channel
CA2948061A1 (en) 2014-05-06 2015-11-12 Huawei Technologies Co., Ltd. Channel boundary locating method, base station, and user equipment
CN105578551B (zh) * 2014-10-08 2019-12-27 展讯通信（上海）有限公司 一种小区切换选择方法及移动终端
US10028279B2 (en) * 2014-12-19 2018-07-17 Futurewei Technologies, Inc. Communications in a wireless network for carrier selection and switching
US11812321B2 (en) * 2015-10-21 2023-11-07 Qualcomm Incorporated Autonomous handover on a shared communication medium
EP3456124B1 (en) * 2016-05-13 2020-01-01 Telefonaktiebolaget LM Ericsson (publ) Tti switching for multicarrier hsupa
WO2018030943A1 (en) * 2016-08-11 2018-02-15 Telefonaktiebolaget Lm Ericsson (Publ) Methods switching frequencies of primary and secondary carriers for multi-carrier communications and related wireless devices and network nodes
US10405281B1 (en) * 2017-06-15 2019-09-03 Sprint Communications Company L.P. Dynamic minimum receiver levels based on carrier aggregation
EP3627878B1 (en) * 2017-07-20 2023-08-30 Guangdong Oppo Mobile Telecommunications Corp., Ltd. Measurement configuration
US20190327655A1 (en) * 2018-04-23 2019-10-24 Mediatek Inc. Methods And Apparatus For Selecting Large-Bandwidth Cell In Mobile Communications
CN109348510B (zh) * 2018-10-17 2021-11-19 中国联合网络通信集团有限公司 负载均衡方法、装置及基站

Family Cites Families (26)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US699333A (en) * 1900-10-03 1902-05-06 Albert Ludwig Vessel for the reception of high-pressure gases.
US6535739B1 (en) * 2000-04-07 2003-03-18 Qualcomm Incorporated Method of handoff within a telecommunications system containing digital base stations with different spectral capabilities
US6993333B2 (en) 2003-10-16 2006-01-31 Flarion Technologies, Inc. Methods and apparatus of improving inter-sector and/or inter-cell handoffs in a multi-carrier wireless communications system
US7308264B2 (en) 2004-02-05 2007-12-11 Interdigital Technology Corporation Method for identifying pre-candidate cells for a mobile unit operating with a switched beam antenna in a wireless communication system, and corresponding system
GB2416269A (en) * 2004-04-16 2006-01-18 Nokia Corp Cell selection and re-selection
JP2005328525A (ja) * 2004-05-04 2005-11-24 Samsung Electronics Co Ltd 上りリンクパケット伝送システムにおけるソフトハンドオーバー端末機の最適のスケジューリングセルを選択するための方法及び装置
KR100933156B1 (ko) * 2004-08-12 2009-12-21 삼성전자주식회사 업링크 서비스를 위한 전송 채널들을 이용한 핸드오프 지역에서의 업링크 데이터 송수신 방법 및 장치
KR100884989B1 (ko) 2004-09-29 2009-02-20 노키아 코포레이션 고속 다운링크 공유 채널 정보로 액티브 세트 갱신
JP4840326B2 (ja) 2005-03-28 2011-12-21 ソニー株式会社 移動端末
US8050222B2 (en) * 2005-03-28 2011-11-01 Sony Corporation Mobile communications system, handover controlling method, radio network controller, and mobile terminal
US8031673B2 (en) * 2005-06-03 2011-10-04 Telefonaktiebolaget Lm Ericsson (Publ) Cell change in cellular networks
KR101256155B1 (ko) * 2005-08-19 2013-04-19 지티이 코포레이션 시분할-동기식 코드 분할 다중 접속 시스템의 다중 캐리어고속 하향 패킷 접속 구현 방법
GB2431070B (en) 2005-10-06 2008-02-13 Samsung Electronics Co Ltd Mobile communications
EP1781057A1 (en) * 2005-10-26 2007-05-02 Matsushita Electric Industrial Co., Ltd. Fast radio bearer establishment in a mobile communication system
US7821996B2 (en) * 2005-10-27 2010-10-26 Motorola Mobility, Inc. Mobility enhancement for real time service over high speed downlink packet access (HSDPA)
JP4895603B2 (ja) 2005-12-22 2012-03-14 京セラ株式会社 通信制御システム、無線通信端末及び通信制御方法
JP4789613B2 (ja) 2005-12-22 2011-10-12 京セラ株式会社 無線通信端末及び通信方法
US20080005797A1 (en) * 2006-06-30 2008-01-03 Microsoft Corporation Identifying malware in a boot environment
PT1886585E (pt) * 2006-07-24 2008-11-03 Unilever Nv Bebida melhorada
US8660558B2 (en) * 2006-08-22 2014-02-25 Telefonaktiebolaget L M Ericsson (Publ) Method for load balancing of devices in idle mode
JP4797888B2 (ja) * 2006-08-31 2011-10-19 株式会社日立製作所 複数の無線リソースを用いて通信する無線通信システム、制御ノード、および基地局
EP1915016A3 (en) 2006-10-20 2010-08-04 Innovative Sonic Limited Method and apparatus for setting configurations of uplink transport channel in a wireless communications system
US8094554B2 (en) * 2006-10-26 2012-01-10 Qualcomm Incorporated Compressed mode operation and power control with discontinuous transmission and/or reception
US20080200202A1 (en) * 2007-02-13 2008-08-21 Qualcomm Incorporated Power control with link imbalance on downlink and uplink
US8670762B2 (en) * 2007-04-18 2014-03-11 Qualcomm Incorporated Fast serving cell change
US7983215B2 (en) * 2008-04-17 2011-07-19 Infineon Technologies Ag Communication device, method for transmitting an uplink transmission control message, method for receiving an uplink transmission control message

Also Published As

Publication number Publication date
KR20150060995A (ko) 2015-06-03
CN103997765B (zh) 2018-07-13
TW201517646A (zh) 2015-05-01
KR101580347B1 (ko) 2015-12-24
CN201657330U (zh) 2010-11-24
KR20110030596A (ko) 2011-03-23
BRPI0909948A2 (pt) 2017-10-31
AR072195A1 (es) 2010-08-11
JP6084958B2 (ja) 2017-02-22
TWI482512B (zh) 2015-04-21
KR101228962B1 (ko) 2013-02-01
TWM378576U (en) 2010-04-11
EP2603043B1 (en) 2015-10-21
KR101633202B1 (ko) 2016-06-23
EP2603043A1 (en) 2013-06-12
EP2720497A1 (en) 2014-04-16
JP2012231539A (ja) 2012-11-22
JP5647193B2 (ja) 2014-12-24
EP2292044A1 (en) 2011-03-09
EP2720497B1 (en) 2016-04-20
WO2009155480A1 (en) 2009-12-23
CN102067672B (zh) 2014-07-16
KR20110111539A (ko) 2011-10-11
EP2292044B1 (en) 2013-08-07
KR20140085602A (ko) 2014-07-07
JP5059971B2 (ja) 2012-10-31
US20100222059A1 (en) 2010-09-02
US9532288B2 (en) 2016-12-27
TW201002108A (en) 2010-01-01
JP2011525336A (ja) 2011-09-15
CN103997765A (zh) 2014-08-20
RU2467513C2 (ru) 2012-11-20
CN102067672A (zh) 2011-05-18
BRPI0909948B1 (pt) 2020-10-13
JP2015073285A (ja) 2015-04-16
TWI566615B (zh) 2017-01-11
US20170048779A1 (en) 2017-02-16
RU2011101682A (ru) 2012-07-27

Similar Documents

Publication Publication Date Title
HK1155312A1 (en) Optimized serving dual cell change
HK1249547A1 (zh) 鹽藻糖基化欠缺細胞
GB0720484D0 (en) Cells
GB0908613D0 (en) T Cell Reseptors
EP2328207A4 (en) BATTERY
IL201102A0 (en) Fast serving cell change
EP2351423A4 (en) CELL CALIBRATION
EP2200112A4 (en) CELL ARRANGEMENT
EP2249646A4 (en) PDE4 muscarinic Antagonist-DOPPELPHARMACOPHOREN
EP2250238A4 (en) BIOFUEL
GB0813669D0 (en) Electrolyte
IL207352A0 (en) Dual pharmacophores - pde4 - muscarinic antagonistics
GB0807863D0 (en) Biodiesel
IL207351A0 (en) Dual pharmacophores - pde4 - muscarinic antagonistics
GB0920775D0 (en) Cells
IL207346A0 (en) Dual pharmacophores - pde4 - muscarinic antagonistics
GB0718490D0 (en) Biodiesel
EP2356040A4 (en) DOUBLE PACKING
EP2249830A4 (en) DUAL PHARMACOPHORES, ANTAGONISTS OF MUSCARINIC RECEPTORS AND INHIBITORS OF PDE4 ACTIVITY
HK1146333A1 (en) Battery
IL244553B (en) Altered placental cells
GB0811353D0 (en) Cell line
GB0810505D0 (en) M cell
GB0700936D0 (en) Cells
GB0816635D0 (en) Cell fusion