1. 1 Title: A Proposal for Identifying Hand-In Femto Cell Sources: ZTE Contact: Yonggang Fang (yfang@zteusa.com), Xiaowu Zhao (zhao.xiaowu@zte.com.cn)yfang@zteusa.com ABSTRACT: This contribution addresses the issue of pilot PN reuse in femto cells deployed in the overlap area with macro cells and proposes an approach using special pilot to identify hand- in femto cells uniquely for cdma2000 1x network. Recommendation: Review and adopt ZTE grants 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. ZTE 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 ZTE 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 contributors. ZTE specifically reserves the right to amend or modify the material contained herein and to any intellectual property of contributors other than provided in the copyright statement above. 3GPP2-C22-20080825-017

2. 2 Background  Introduction PN confusion issue was identified in the reference [1] [2] [3] Reuse of pilot PN code of femto cells in the overlap area with macro cell might be possible to cause PN reuse confusion. This confusion makes the macro cell not be able to distinguish target femto cell when a mobile station is performing hand-in process, and would result in the hand off failure. In reference [1], three options were proposed to use a special pilot to provide additional identification of HRPD femto cell. Option 1 pre-defines an algorithm of special pilot PN generation. FAP autonomous transmits special pilot for AT to detect using the same algorithm. This option has the least touch on the existing macro AN. Option 2 needs macro AN to send message to femto AP to trigger the special pilot transmission Option 3 is to optimize the option 1 via macro AN control so as to reduce the interference generated by femto cell’s special pilot. In this contribution, a similar solution of using special pilot PN sequence is proposed to address the issue in cdma2000 1x network.

3. 3 Background  CDMA2000 1x Walsh channels Unlike HRPD, cdam2000 1x uses different Walsh channels to carry different information on forward link, such as W 0 is for pilot, W 1-7 is for Paging channels, W 32 is for Sync channel, etc. Auxiliary Pilot is spread by a Walsh code assigned by base station For Spreading Rate 1, the number of Walsh codes used for Auxiliary Pilots is 128 For Spreading Rate 3, the number of Walsh codes used for Auxiliary Pilots is 256 Walsh codes can be extended to 512 through concatenation from basic Walsh codes 

4. 4 Special Pilot Sequence for 1x  Use Special Pilot to Identify Femto Cell Similar to mechanism in reference [1], we propose to use Walsh code modulated the special pilot to provide additional information of FAP for mobile station to detect and report to the macro BS.  Walsh Channels The special pilot could be transmitted on existing Walsh channels or extended Walsh code channels in order to reduce the impact on existing applications.  Walsh Channel Hopping FAP transmits the special pilot over different Walsh channel in every frame(s) The simplest case is no hopping of Walsh channel, like the auxiliary pilot. FAP determines the hopping pattern of Walsh channels based on Frame number index and FAP ID The transmission of special pilot could be controlled by ether Macro BS when there is PN code confusion or FAP, i.e. autonomous continuously transmitting

5. 5 Special Pilot Sequence for 1x  Detection of Special Pilot over Walsh channels Mobile station continuously detects special pilot on the Walsh channels over a certain frames Based on the Walsh channel hopping pattern of special pilot, mobile station would derives FAP ID  Reporting Mechanism Mobile station would report the detected special pilot (Walsh sequence) in Candidate Frequency Search Report, or updated PSMM/PMRM to the macro BS. The macro BS coverts the special pilot sequence to the FAP ID. Or Mobile station would convert the detected special pilot into FAP ID and report in CFSR, or updated PMRM message.

6. 6 Special Pilot Sequence for 1x  Walsh Hopping Sequence For the Special Pilot A Walsh hopping sequence is a sequence of Walsh codes with length n, which is transmitting in sequential in time domain Each Walsh code used to form Walsh hopping sequence is from Walsh code set C The length of Walsh hopping sequence n and Walsh code size m depends on the number of femto cells to be deployed in the overlap area with macro cell. It could be fixed length or broadcast in the overhead channel The longer length n of Walsh hopping sequence and larger Walsh code set size m, the more reuse PN code of femto cells allowed, but longer time for detecting complete special pilot sequence

7. 7 Special Pilot Sequence for 1x Femto Cell - 1 Frame i Frame i+ 1 Frame i+ 2 Mobile station report the detection result to the macro BS Wi = aWi+1 = bWi+1 = c Femto Cell - 2Wi = aWi+1 = d Wi+1 = f Example of special pilot detection by mobile station For n = 3, mobile station needs to detect three continuous frames to get special pilot on the hopped Walsh channels.

8. 8 Special Pilot Sequence for 1x  Femto Cell PN Space Extension Walsh code size: m Walsh hopping sequence length: n Number of Pilot PN codes for femto cells: The umber of femto cells per macro-cell: m=64m=128 n = 164N 0 128N 0 n = 2 N 0 n = 3 N 0 For the simplest case, like n = 1, m=128, the femto cell PN code space is expanded 128 times of current usable PN codes for femto cells.

9. 9 Proposed Message Changes  Neighbor List Message Existing Private Neighbor List Message may be used for the legacy mobiles Updated ENLM to include auxiliary pilot. Macro BS sends to individual mobile station during the handover.  Power Measurement Report Message Existing Candidate Frequency Search Report message may be used for the legacy mobiles Update the existing PMRM to include the auxiliary pilot information Femto mobile station may respond macro BS request or periodically report the measurement on the special pilot.

10. 10 Summary  Summary This contribution proposes a solution to identify the hand-in femto cell uniquely via special pilot PN sequence for cdma2000 1x network. The special pilot PN sequence is carried over a set of Walsh code channels Less impact on existing cdma2000 1x spec. The simplest case is compactable with existing cdma2000 1x specification. For the intra-frequency handoff, it would be possible not to have measurement gap so as to maintain the existing call continuity during the candidate frequency/pilot search. The proposal supports scalability of femto PN expansion for future enhanced cdma2000 1x femto network and mobile station. The special pilot PN sequence could be periodically transmitted by FAP based on the pre-defined algorithm, or controlled by the network when macro AN finds the confusion on the FAP regular PN code.

11. 11 References  Reference 1. C20-20080721-023_ZTE_Femto-PN-Indentification 2. C20-20080721-020 cdma2000 1x Signaling Enhancements for Femto AP Support (AQ) 3. C30-20080721-023-QC Femto Interference Mgmnt and Design Considerations