1. 1 Call-back HO Procedure for Reentry Femtocell Document Number: IEEE C802.16m-08/1438r1 Date Submitted: 2008-11-05 Source: Yung-Ting Lee, Hua-Chiang Yin E-mail : yungting.lee@coiler.com.tw Coiler Shiann-Tsong Sheu, Chih-Cheng Yang National Central University (NCU) Whai-En Chen National Ilan University (NIU) Kanchei (Ken) Loa,Yi-Hsueh Tsai, Chun-Yen Hsu,Youn-Tai Lee Institute for Information Industry (III) 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: IEEE 802.16m-08/003r5 Purpose: For discussion and approval by IEEE 802.16m Working Group 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 IEEEs name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEEs 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. Problem Statement Since the femtocell backhaul link may disconnect from network and reconnect to network sometimes, the method for handling the associated MSs to leave and return the femtocell should be designed in order to –continue the services, and –optimize the network performance.

3. Handover Trigger The WiMAX Forum document Requirements for WiMAX Femtocell Systems states that –A Femto BS SHALL disable its downlink air interface transmitter until the connection with the operators network is fully established. As the serving femtocell loses the backhaul connection, it shall command all the associated MSs to perform handover procedure. –The handover request signal shall include the reason code, which is used to notify the MSs to record the original Femto BS information and wait for any callback signal.

4. Call-back handover procedure As the femto BS reconnects to the network again, the femto BS or the network HO controller initiates the call-back handover procedure to generate the callback HO message with the original femto BS ID for related BS in order to call back those MSs who have recorded the information of original femto BS. Upon the MS receiving the call-back handover signal from serving BS, it will try to handover to the recorded femto BS if the signal quality is better than the current connection.

5. Call-back handover procedure (case 1 : femtocell initiated) Femto BS MSMacro BS/Femto BS Lost backhaul link MOB-HO_REQ MOB-HO_IND HO to target BS Recover backhaul link MOB-CallBack_HO_REQ (via backhaul link) MOB-CallBack_HO_REQ HO to original BS MOB-CallBack_HO_RSP (via backhaul link) MOB-CallBack_HO_IND

6. Call-back handover procedure (case 2 : network handover controller initiated) Femto BS MSMacro BS/Femto BS Lost backhaul link MOB-HO_REQ MOB-HO_IND HO to target BS Recover backhaul link MOB-CallBack_HO_REQ HO to original BS Network HO controller Re-register to network via backhaul link MOB-CallBack_HO_RSP MOB-CallBack_HO_IND

7. Proposed Text [Add the following sections 17.x.1 Handover Request Support and 17.x.2 Call-back Handover Support] 17.x.1 Handover Request Support As the femto BS loses the connectivity of backhaul link, it shall send the handover request signal with reason code to all associated MSs. All the notified MSs shall perform handover procedure to re- associate with the designated BSs, if any. 17.x.2 Call-back Handover Support Upon the backhaul connectivity is recovered, the femto BS and/or the network handover controller may issue call-back handover signals with femto BS ID to the related BSs for notifying those MSs, who have stored the information of femto BS, to handover back.