March 2011 C2 – Company Confidential SOURCE: Jialin Zou, David Rossetti, Satish Kanugovi (Alcatel-Lucent) satish.k ABSTRACT: When Femtocell cannot access GPS signals to derive accurate timing, it can communicate with the neighboring macrocell to derive the timing correction. TITLE: Timing Synchronization of a femtocell using the neighboring macrocell 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 Macrocell signals have better penetration as compared to GPS. Often, even though there is no usable GPS signal, there may be a weak CDMA signal available. Femtocell is able to listen to the neighboring macrocells and communicate with them

C2 – Company Confidential 5 | CDMA Femtocells | March 2011 Proposed solution  Femtocell can measure the pilot channel of the neighboring macrocell(s)  Femtocell would know the PN offset at which the neighboring macrocell is configured to transmit pilots  Monitor paging/control channel of the neighboring macrocell  By provisioning (Femto management system)  The received PN offset from the macrocell and the actual PN offset (found in step above) would be different due to the inaccuracy/drift of Femtocell’s own timing  Femtocell can estimate the timing offset at which it should receive the pilot from the macrocell from the knowledge of PN offset and the round trip delay  Compare this with PN timing actually received from the macrocell and calculate the discrepancy  The discrepancy so calculated can be used to correct the internal clock at the femtocell

C2 – Company Confidential 6 | CDMA Femtocells | March 2011 Proposed solution  Create a signaling message to enable femtocell to get Round Trip Delay information  Femtocell uses the following to calculate its internal clock drift  The round trip delay with the macrocell  Received pilot PN timing from the macrocell  Knowledge of actual PN offset  Correct internal clock with the value of the drift