1. 1 Title: Active HO optimization from eHRPD to LTE Abstract: This contribution supersedes “C22-20110523-014r1 ZTE C.S0087-eAT-based- redirection” which provides one approach for active HO optimization from eHRPD to LTE. Recommendation: Review and Adopt for C.S0087-A v2.0 Source: Yuanfang Yu, Ting Lu, Yonggang Fang, Xiaowu Zhao Yu.yuanfang, lu.ting@zte.com.cn

2. 2 eHRPD to LTE active Handoff Current C.S0087 only defines idle handoff from eHRPD to LTE However, redirecting eATs during active mode might be helpful for the following scenarios: –Load balancing –Handoff from eHRPD to LTE when LTE is available. Proposals –Option 1: Refer to QC/ZTE/CT joint contribution –Option 2: Redirection controlled by AT with AN assist in this contribution

3. 3 Proposal – Redirection controlled by AT with AN assist

4. 4 Redirection controlled by AT with AN assist AN sends redirect indicator through OtherRATNeighborList message while AN wants UEs to handoff from eHRPD to LTE –AN provide the reasonable redirect threshold to UE, once the strength of LTE channel meets the condition, UE will redirect to LTE –Key points AN decides the timing of setting redirect indicator and the threshold for redirect in OtherRATNeighborList message –AN decides its redirect indicator based on its requirement, e.g. high traffic load, special application, energy saving operation and so on, but final redirect decision is made by UE based on its conditions AN unicast OtherRATNeighborList message through Traffic channel UE performs redirect when conditions meet, otherwise UE still in eHRPD

5. 5  Enhanced OtherRATNeighborList message FieldLength (bits) MessageID8 OtherRATSignature6 NumOtherRAT4 NumOtherRAT occurrences of the following field { RATType4 NeighborRATRecordLength10 NeighborRATRecord8*NeighborRATRecord Length } RedirectIndicatorIncluded1 NumOtherRAT occurrences of { RedirectToThisRAT0 or 1 ReturnIfFail0 or 1 } Reserved0 – 7 (as needed)

6. 6 Analysis for comments Comment 1: benefits of unicast OtherRATNeighborList message –AN could inform its redirection requirement to eAT. –The unicast OtherRATNeighborList message could transfer a set of handoff threshold parameters which may be differ from that including in broadcast OtherRATNeighborList message to an active eAT to assist it doing active handoff. –The modification to eHRPD network is minimize.

7. 7 Analysis for comments Comment 2: Ping pong issue –Since initial LTE deployment only covers hot spots area, it can thought eHRPD has bigger coverage and better signal than LTE, therefore no matter LTE->eHRPD or eHRPD- >LTE mainly depends on LTE signal strength, as the figures show, it is reasonable that the threshold1 for triggering LTE->eHRPD handoff is smaller than threshold2 for eHRPD- >LTE handoff. There is a gap between these two thresholds, in this proposal, when unicast OtherRATNeighborList, if the threshold for eHRPD->LTE handoff might be at the range between threshold1 and threshold2, the pingpong can be avoided.

8. 8 Analysis for comments Comment 3: conflict between unicast and broadcast otherRATNeighborList message –Unicast message always has higher priority than broadcast message, so when UE in connected state receives unicast OtherRATNeighborList, it should ignore the broadcast OtherRATNeighborList; –When UE performs LTE measurement in this contribution, it still maintains in eHRPD connected state, the above criteria always works; –Once LTE signal strength meets the redirection condition (refer to comment 2), UE will redirect to LTE, it does not need to enter eHPRD idle to receive HRPD overhead messages; –If LTE signal strength does not meet the redirection condition, UE should maintain eHRPD connection. If UE return the eHRPD idle state after ending of service, it can receive broadcast OtherRATNeighborList and overrides all parameters before.

9. 9 Pros and Cons of Proposal Pros –Minor modifications for AT and AN to support redirection function –Sending TCH OtherRATNeighborList message with redirect indication allows UE to get LTE paras and perform LTE measurement more quickly than broadcast mechanism –not handling LTE mesurement results can simplify AN’s procedure and not reporting LTE measurement result to AN can simplify AT’s procedure Cons –Since final redirection decision depends on UE’s measurement results, it is not mandatory redirection