1. Interference mitigation in Femtocell Document Number: IEEE C802.16m-08/1427r2 Date Submitted: 2008-10-31 Source: Kaibin Zhang, Gang Shen, Jimin LiuVoice:+86-21-50554550-8261 Alcatel Shanghai Bell Co., Ltd.E-mail: kaibin.zhang@alcatel-sbell.com.cnkaibin.zhang@alcatel-sbell.com.cn Hongyun Qu, Huiying Fang, Yuqin Chen ZTE qu.hongyun@zte.com.cnqu.hongyun@zte.com.cn Xiaolu Dong, Ying Du, Daning Gong CATRdongxiaolu@mail.ritt.com.cndongxiaolu@mail.ritt.com.cn Xin Su, Xiaofeng Zhong Tsinghua Universitysuxin@mail.tsinghua.edu.cnsuxin@mail.tsinghua.edu.cn Hangfeng Zhang, Zhuo Gao Datang Mobilezhanghanfeng@datangmobile.cnzhanghanfeng@datangmobile.cn Venue: IEEE 802.16m-08/040: Call for Comments and Contributions on Project 802.16m System Description Document (SDD), on the topic of TGm SDD: Femtocells Base Contribution: N/A Purpose: To be discussed and adopted into the 802.16m SDD by TGm. Notice: This document does not represent the agreed views of the IEEE 802.16 Working Group or any of its subgroups. It represents only the views of the participants listed in the “Source(s)” field above. It is offered as a basis for discussion. It is not binding on the contributor(s), who reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.16. Patent Policy: The contributor is familiar with the IEEE-SA Patent Policy and Procedures: and.http://standards.ieee.org/guides/bylaws/sect6-7.html#6http://standards.ieee.org/guides/opman/sect6.html#6.3 Further information is located at and.http://standards.ieee.org/board/pat/pat-material.htmlhttp://standards.ieee.org/board/pat

2. Introduction Femtocell –Femtocell, tiny, low-power cellular base stations, operated in licensed frequencies. –A femtocell installed in homes or SOHO, typically overlapped with macro-cells to improve the indoor coverage by providing the coverage up to 30m. –Using existing wired broadband connection as backhaul (cable, DSL, Ethernet) Scenarios to be considered –Open access Femto serves any MS within the coverage –Closed access Femto only serves the MS subscribed with it

3. Interference scenarios in overlapped networks Macro Femto –Frequency shared by macro and Femto Mutual co-channel interference –Dedicated frequency for Femtocell No interference Femto –Co-channel interference if spectrum reusing Femtocell Macro-cell BS Femtocell

4. Downlink Interference of femto -> macro macro MS interfered by Femtocell Outdoor macro users may experience interference by nearby indoor Femtocell –Femto installed near houses boundary, penetration/leakage through windows will cause interference to outdoor macro users near houses –In order to cover whole house, femtocell has to enhance/boost its tx power, which would increase the interference to outdoor nearby users. Indoor macro users may be interfered by Femtocell –In closed access scenario –DL signal from Femtocell is much stronger than that from macro BS for indoor users, which may prevent indoor macro MS from decoding signals from macro BS –There might be a dead zone around Femto BS within which macro MS can not connect to macrocell Leakage from indoor Femto interfere with nearby outdoor DL signal Femto DL strongly interferes indoor macro MS from connecting macro BS macro MS Macro MS Femto MS Femto BS macro BS

5. Uplink Interference of macro to femto Indoor macro MS may interfere with indoor femto MS –High tx power of indoor macro MS, due to big path loss and wall loss, especially at cell edge –Low tx power of indoor Femto MS, due to short distance –High UL signal strength from indoor macro MS may prevent indoor MS from connecting to Femtocell in UL Femtocell experiences interference from strong macro MS UL signal Macro MS Femto MS Femto BS macro BS

6. Solutions to interference mitigation Interference detection & mitigation –Femtocell BS should have the capability to estimate the surrounding potential interference based on scanning the neighboring Femtocells and macro-cell –Femtocell BS estimates and reports the interference from all neighboring cells to NCMS(Network Control & Management System) or Femto gateway –The NCMS shall coordinate with macro BS and neighboring Femto BSs to mitigate the interference based on the scanning results from Femto BS as well as MS Interference mitigation approaches may include –Assigning appropriate frame partitions or subframes different from neighbors –Adjustment of transmitting power It could be performed –Once a Femto BS initiates itself –Periodically to adapt to the changing environment Femto BS may perform periodical interference detection when the attached MSs are in idle/sleep unavailable intervals

7. Proposed Text For SDD 17 Support for Femtocell 17.x Interference mitigation Femto BS shall measure the surrounding interference by scanning the neighboring Femtocells and macro-cell. MS shall also perform measurement and report the results. The measurement may be performed periodically. The interference mitigation approaches shall be performed by Femtocells and macro-cells under the coordination.