March 2011 C2 – Company Confidential SOURCE: Jialin Zou, David Rossetti, Satish Kanugovi (Alcatel-Lucent) satish.k ABSTRACT: AT assisted synchronization of femto cells is an low cost efficient method which could be considered as an alternative solution for femto synchronization. TITLE: AT Assisted Synchronization of A Femto Cell with The Umbrella Macro Cell TSG-C RECOMMENDATION: Discuss and adopt. The source companies of this contribution grant a free, irrevocable license to 3GPP2 and its Organizational Partners to incorporate text or other copyrightable material contained in the contribution and any modifications thereof in the creation of 3GPP2 publications; to copyright and sell in Organizational Partner's name any Organizational Partner's standards publication even though it may include all or portions of this contribution; and at the Organizational Partner's sole discretion to permit others to reproduce in whole or in part such contribution or the resulting Organizational Partner's standards publication. The source companies of this contribution is also willing to grant licenses under such contributor copyrights to third parties on reasonable, non-discriminatory terms and conditions for purpose of practicing an Organizational Partner’s standard which incorporates this contribution. This document has been prepared by The source companies of this contribution to assist the development of specifications by 3GPP2. It is proposed to the Committee as a basis for discussion and is not to be construed as a binding proposal on The source companies of this contribution. The source companies of this contribution specifically reserves the right to amend or modify the material contained herein and to any intellectual property of The source companies of this contribution other than provided in the copyright statement above.

C2 – Company Confidential 2 | CDMA Femtocells | March 2011 Background and Motivation CDMA basestations, macrocells and femtocells, require accurate timing information for their operation Timing is typically derived using GPS Femtocells can deployed in indoor locations where GPS signals penetration is poor In-door small cells/ femto cells have difficulties to acquire the GPS signals  The strength of the GPS signals indoor are 30 dB lower than that of outdoor macro  Hence, the femtocells cannot rely on GPS to derive timing  More efforts are required for the indoor small/femto cells to achieve the synchronization

C2 – Company Confidential 3 | CDMA Femtocells | March 2011 Background and Motivation Some of the possible solutions  Build in a GPS receiver and use an external antenna to receive the GPS signals  Get synchronization with the network through backhaul

C2 – Company Confidential 4 | CDMA Femtocells | March 2011 Background and Motivation Consider a low cost option for the indoor access point (AP) acquiring the system timing from a mobile  Assume at least the in-door small/femto cell border area is also covered by the macro cell  Assume the AT is already synchronized with the macro cell

C2 – Company Confidential 5 | CDMA Femtocells | March 2011 Proposed solution

C2 – Company Confidential Proposed solution Triggered by the request from the serving macro BTS or the AT internal femto information, the AT measures the femto AP PN offset  BTS may send out the FAP measurement request at the FAP power up/initial calibration phase (the user with the AT are expect being very close to the FAP)  After the initialization, the AT memorizes the FAP related information such as fingerprint, proximity … which could trigger the AT to start the FAP measurement The AT reports PN offset of the FAP together with power measurement, and possibly the AT location to the serving macro BTS  With the AT close enough to the FAP, the AT measured FAP PN offset can be consider the offset relative to the serving pilot arrived at the FAP The BTS forwards the AT reported FAP PN offset, the macro cell PNOffset  BTS determines when to forward offset information -- FAP power measurement should be above a threshold, measured PN offset should be above a threshold After the FAP receives its PN offset measured the AT via network, it will remove the offset due to Drifting: Offset_ Drifting  PN_offset_ measured = PNOffset_ FAP - PNOffset_ macro – OWD_ AT + Offset_ Drifting + OWD_ FAP ~= PNOffset_ FAP - PNOffset_ macro + Offset_ Drifting  Since the clock drifting of the FAP is very slow, long delay (even tens of seconds) is tolerable for delivery of the PN offset to the FAP 6 | CDMA Femtocells | March 2011

C2 – Company Confidential Proposed solution Some required possible standards changes  Define a new AI message from BTS to the AT, i.e. request the AT to report the femto PN offset  In the measurement report (e.g RUM), femto measurement report will be indicated for differentiation  Define the network message to carry the offset information from the macro BTS to the FAP  Define the related procedures Note: Additional information could be also delivered to the FAP  With the AT close enough to the FAP, the AT’s OWD and location can be considered the same as the FAP’s OWD and location  AT assisted FAP OWD estimation could be used in many applications even for the femto sniffing macro case  AT assisted location estimation could be used as the FAP location 7 | CDMA Femtocells | March 2011