1 Discussion on Handoffs for 1x/HRPD Femtos Peerapol Tinnakornsrisuphap David Ott Chandru Sundarraman Qualcomm July 21 st, 2008 Recommendation: FYI Notice QUALCOMM Incorporated 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. QUALCOMM Incorporated 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 QUALCOMM Incorporated 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 QUALCOMM Incorporated. QUALCOMM Incorporated specifically reserves the right to amend or modify the material contained herein and nothing herein shall be construed as conferring or offering licenses or rights with respect to any intellectual property of QUALCOMM Incorporated other than provided in the copyright statement above.

2 Introduction This contribution explores the feasibility of handoff between femto APs and macro ANs in both 1x and HRPD Main issues to be explored are –Reachability How do source/target find each other? –Scalability Fundamental limitations on the scheme (per standard) –Any additional standardization needed? E.g., availability of information in messages

3 1x Femto Architecture Diagram (from PDS)

4 HRPD Femto Architecture Diagram (from PDS)

5 1x Idle Handoff from Macro -> Femto Reachability –MS registers directly with MFIF through the target femto Scalability –No problem identified Additional Standardization Need –None in TSG-A

6 1x Connected Handoff from Macro -> Femto Reachability –Currently in 1x, BS maps PN to target CellID, Sector and MSCID in the A1-Handoff Required message to MSC –Macro 1x BS needs to be able to determine CellID and MSCID of Femtocell –Each Femto AP needs to be assigned CellID and MSCID and this information is included in the FemtoID message –The Pilot Strength Measurement Message needs to be enhanced to include CellID and MSCID or FemtoID needs to include this information –MFIF needs to be assigned with MSCID and Legacy MSC needs to route to it on IS-41 Scalability –CellID has 12 bits = 4096 femtos per CSRV, however, one MFIF may be assigned multiple MSCID if necessary. MSCID is 24 bits long. Additional Standardization Need –Air-interface enhancement to support communication of MSCID and CellID of femto AP to MS (in broadcast message from femto) –Enhancement to Pilot Strength Measurement Message to contain the above information

7 Active Call Hand-in Ambiguity Under the same macro BS, it is likely that the same PN will be assigned to many Femto APs Macro BS needs to be able to resolve target MSCID and CellID for the PN that has ambiguity Femto AP is configured with unique MSCID and CellID. This information is advertised in the Femto ID message. The MS includes this info with the PSMM. The remaining standard handoff process will route the call to the MFIF (based on MSCID) and correct femto AP (based on CellID) with no modification to A1 and IS- 41 interfaces Macro BS PN = a Femto AP1 PN = b Femto AP2 PN = b MSC MFIF 2. PSMM + 3. A1-Handoff Request 4. IS FIDM (MSCID, CellID) 5. MFIF contacts Femto AP2 for handoff

8 HRPD Idle Handoff from Macro -> Femto Reachability –Based on UATI32, Femto can locate macro AN Need mapping from CC:UATI24 to UATI128 and macro AN IP address at Femto –Femto finds Macro AN and perform A13 handoff Scalability –No problem identified Standardized –IP address lookup scheme from to IP address of AN and also to UATI128 –If Femto connects to different PDSN, PPP needs to be renegotiated. This can be avoided with PDSN Fast Handoff

9 HRPD Idle Handoff from Femto -> Macro Reachability –Macro AN advertises different ColorCode from Femto AP, so AT is triggered to register with macro AN –Since AT only sends 8 bits ColorCode + 24 LSBs of UATI in access capsule, macro needs to be able to map these information into Femto AP IP address –See next slide Scalability –See next slide Additional Standardization Need –IP address lookup scheme from CC:UATI24 to IP address of Femto and also to UATI128

10 HRPD Idle Handoff from Femto -> Macro or Femto -> Femto : UATI, ColorCode and Subnet Number of users that can be supported in a Femto = 2 C Number of Femtos that can be supported in a ColorCode = 2 24-C In order to resolve IP address of Femto, the following information are needed –Number of bits for C –Mapping from ColorCode to Subnet Mask in the geographical area –Mapping from BSC_ID to IP address of Femto BSC_ID maybe IP address of Femto, however, the private IP address assigned from operator to Femto cell in the same vicinity and same ColorCode needs to have same 8+C MSBs of IP address If two Femtos next to each other has same ColorCode, dormant handoff would not be triggered –That might not be a problem. When connection is requested, the target Femto can still request session from source Femto. This eliminates need to constantly request UATI from Femto –Need A13-Paging support between Femtos AT-specificBSC_ID_LSBBSC_ID_MSB Subnet Mask 104 bits (maps to 8 bits ColorCode) C bits24-C bits UATI128

11 HRPD Connected Handoff from Macro -> Femto Reachability –AN needs to be informed of the SectorID or FemtoID of the target Femto, then the macro AN can map the information to IP address of the target Femto Could be through DNS lookup Scalability –None identified Additional Standardization Need –DNS lookup and update scheme between Femto, DNS server, and macro AN for FemtoID/SectorID

12 HRPD Connected Handoff from Femto -> Macro Reachability –Femto AN needs to be configured with the mapping between PN of the neighboring macro sector and Macro AN IP address Information in messages –If PN is being repeated under the same macro BSC, the BSC may be confused of which sector to assign resources to Additional Standardization Need –How Femto learned of macro PNs in the area and macro AN IP addresses –A16 needs to be enhanced with target sectorID to avoid confusion in case macro AN reuse same PN