1. Mobility Support in Femtocell Document Number: IEEE C802.16m-08/1431r1 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 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, improves the indoor coverage by providing the coverage up to 30m. –Typically using existing wired broadband connection as backhaul (cable, DSL, Ethernet) Scenarios to be considered –Femtocell overlapped with macro-cell -  Full coverage Frequency shared by macro and femto –High spectrum efficiency, potential interference Dedicated frequency for femtocell –No co-channel interference, but less efficiency –Discrete femtocells w/o macro overlapping Seldom using, not considered in this contribution

3. Mobility issues to be considered Handover scenarios related to Femtocell –Macro->Femto, Femto->macro, Femto Femto Technical issues –Neighboring notification & scanning Long time and larger signaling overhead if broadcasting neighboring list due to the large number of neighboring Femtos Number of Femtos is greater than the upper limit of size of neighbor list –Ineffectual HO attempts A Femto only support very few users, other handover attempts will be rejected, which introduces much signaling load over air interface –Paging Put hundreds of Femto BS in a paging group may cause much overhead

4. Proposed solutions The neighboring list of a macro cell is classified into two parts, the neighboring macro-cells and neighboring/ overlapped Femtocells The neighboring macro-cells list shall be sent to MS via broadcast –Same as usual, no impact on solutions w/o Femto The neighboring Femtos list shall be sent to MS via unicast –The neighboring Femtos may only include the Femtocells close to the MS, so that the overhead can be reduced. –The neighboring Femto list may be determined based on the network topology –When the MS moves within the coverage of macro-cell, the neighboring Femto list may be updated by macro BS or other network control entity The Femtocells not supporting more users shall not be included in the neighboring Femtocell list –Ineffectual handover attempts are avoided

5. Proposed solutions If an MS performs handover from a macro-cell to a Femtocell, the context of the MS shall be kept at macro BS, instead of removed. –Speed up the handover from Femtocell back to macro-cell Authentication, ranging, registration may be omitted Two methods to support paging in Femtocells –Femto BS performs paging as a normal macro BS Signaling overhead over backhauling –MS may get the paging messages from the macro BS directly. Femto BS is not included into the paging group Simple application and less overhead

6. Proposed Text For SDD 17 Support for Femtocell 17.x Mobility The major handover process shall follow the description in section 10.3, except the following: –The neighboring macro-cell list shall be sent out via broadcast while the neighboring Femtocells list may be sent to an MS via unicast. The neighboring Femto list may only include the Femtocells close to the MS. The Femtocells w/o the capability to support more users shall be excluded from the neighboring Femtocell list. –For an MS performing handover from a macro-cell to a Femtocell, the context of MS shall be kept at macro BS, instead of removed. –Femto BS may not be included into the paging group and not be involved in the paging process, such that an MS in a Femtocell may synchronize to and get the paging messages from the overlapped macro BS directly once the idle mode of this MS is initiated.