Handoff Trigger via Access Channel

1. Handoff Trigger via Access Channel Lucent Technologies Bell Labs Innovations 67 Whippany Road Room 4C-258 Whippany, NJ 07981 Telephone 973-386-5123 Facsimile 973-386-2735 cyhuang@lucent.com ChingYao Huang

2. Assumptions • Since the HTAC will follow the same setup process of the access probe handoff, access handoff and channel assignment into soft handoff (handoff direction message in HTAC), the performance will be based on the studies of IS-95B access performance • It was understood that call drop scenarios might be different from access failures but this study can be used to address the performance improvement when the call drops are caused by temporally missing legs

3. Delay Scenarios • To capture the performance impact by the delaying of pilot active set update, we consider three different update scenarios: • Dynamic update • The ACCESS_HO_LIST can be added to (up to 6 pilots) and replaced by the pilots not in the list • Static update • The ACCESS_HO_LIST will NOT be added to or replaced by new pilots not in the list • The pilot strength of the pilots in the original list will be updated • Add-only update (alternative) • The ACCESS_HO_LIST can be added to (up to 6 pilots) but NOT replaced by the pilots not in the list

4. Simulation Models • The simulations are based on the field data measurement • Call setup failures were identified in the call processing level • A total of 66 call setup failures were captured in the field test • Assumptions: • A set-up call can be saved if the new pilot (or aggregated pilots) > - 12dB • Given that the real call can be successfully continue the call on the traffic channel

5. Call Setup Failure Statistics • Total number of call setup failures: 66 • Call failure distribution (categorized by IS-95B features) • Access Probe HO State: 37.9% • Access HO State: 9.1% • CAMSHO State: 53.0% • The distribution will be varied from market to market

6. Feature Improvements • Access Probe Handoff has the most impact by changing the dynamic update to the static update • The success rare reduces from 96% to 64% • Access probe handoff can benefit the most improvement if the failures were happened in the access probe state • 96% access probe state failures can be resolved by the access probe handoff • The delay of having the pilot update can degrade the success rate of each access improvement feature • Correct active set is important even in the soft handoff legs cases • Failures will increase if the active set information is outdated • The outdated range is in the order of 1 to 2 seconds

7. Delay Performance Studies • The actual improvement may vary from market to market • Performance is not degraded in the add-only update case

8. HTAC timing • Camp on the traffic channel after stop Tx: can be the same as Rescue Channel • The call set up timing measured from overhead information update to the MS sends Service Connected Message always less than 2 seconds. HTAC timing should always shorter than that of call setup. • Time interval apply to HTAC: • Camp on the traffic Channel: ~ 400-600ms (same as Rescue Channel) • Overhead information update - ~ 450ms for call setup. • Not always needed for HTAC. If needed, only Access Parameters is required. • Access Probe (MS sends access probe and receives BS Ack): • 97% successful in the first probe based on field data: < 100ms • 3% 2 - multiple probes: ~ 400ms. • Send HDM and setting up traffic channels for Soft Handoffs: about the same as adding Recsue Channels to the active set.

9. Summary • Since HTAO has the similar mechanism as compared to IS-95B access improvement features, we believe that the improvement studies for IS-95B access features can be used to estimate the HTAO performance • If the call drops (or access failures) are due to wrong pilots (or the pilot is only available later), the HATO can improve most of the failures • A correct pilot information is important to guarantee if the call can setup soft handoff legs • Even interference impact is not considered here, we believe that the interference impact caused by extra access attempts should be less than the impact caused by setting up extra legs