Jeff Bonta Senior Member Of Technical Staff

1. Rescue Channels A Technique To Reduce Dropped Calls Jeff Bonta Senior Member Of Technical Staff

2. Technique For Reducing Dropped Calls • Fundament Problem Leading To Dropped Calls • Mobile and Infrastructure Can’t Communicate • Solution: Rescue Channels • Mobile and infrastructure prearrange possible meeting places to rescue the call • Empower mobile to establish soft handoff with rescue cell on a reserved “rescue channel” • Rescue cells wait for mobile when RF link fails • No messages exchanged. Communication via in-band signaling

3. Illustration : Step 1 Cell 5 Cell 1 tells MS, “If you have trouble, tune to cell 5 or 9 using reserved channel” MS Cell 9 Cell 1 Life is good. Easy to communicate.

4. Illustration : Step 2 Cell 5 Oh no! I can’t talk to MS MS BSC tells cells 5 & 9, “Listen for the MS” Cell 9 BSC Cell 1 Life is chaotic. Can’t communicate.

5. Illustration : Step 3 Yahoo! I can hear the MS Cell 5 Cell 5 or 9, can you hear me? “MS! Can you hear me?” MS “Yes cell 5. I can hear you!” I don’t hear the MS Cell 1 Cell 9 Good life restored. Good communication.

6. Timeline Of Typical Troubled Call MS Disables Transmitter MS Enables Transmitter Frame errors begin ... ... ... ... Call continues 12 bad frames MS receives Neighbor List Update following handoff or origination 2 good frames

7. Timeline Of Typical Dropped Call MS Disables Transmitter MS may promote pilot to candidate set Call Drops Frame errors begin ... ... ... ... 12 bad frames MS receives Neighbor List Update following handoff or origination 5 second Fade Timer (2 consecutive good frames not received)

8. Timeline Of Rescue Channel Concept MS promotes candidate to active set and enables transmitter MS Disables Transmitter New BS receives MS and enables transmitter. MS receives new BS on reserved Walsh code. Call Drops Call continues MS promotes pilot to candidate set Frame errors resume ... ... ... 12 bad frames MS receives Neighbor List Update following handoff or origination (includes rescue candidate information) Settable timer

9. Rescue Channel Timeline (rescue scenario: successful rescue) MS disables transmitter Neighbor > T_ADD. Promotes neighbor to active set, MS enables transmitter, and sends PSMM. Cancels rescue allowed timer. MS locks finger on rescue cell(s) and receives N3M good frames. Re-key timer cancelled. Closed loop power control stops MS Events/Actions Rescue re-key timer Frame errors begin Rescue delay timer Rescue allowed timer 12 bad frames … ... Call continues … ... 2 good frames 8 bad frames BSC Events with Sample Actions Rescue cell(s) finger acquires MS and enables transmitter. BSC receives PSMM w/rescue flag set, and cuts path thru Rescue cells begin listening to MS waiting to lock a finger on MS BSC selects rescue cell(s) and begins preparation for rescue

10. Rescue Channel Timeline (rescue scenario: unsuccessful rescue) MS enables transmitter Neighbor > T_ADD. Promotes neighbor to active set, MS enables transmitter, and sends PSMM. Cancels rescue allowed timer. MS fails to receive N3M good frames. MS disables transmitter. Closed loop power control stops MS Events/Actions Rescue re-key timer Frame errors begin Rescue delay timer Rescue allowed timer Call drops if fade timer expires 12 bad frames … ... … 8 bad frames Rescue acquire timer BSC Events with Sample Actions Rescue cells begin listening to MS waiting to lock a finger on MS BSC selects rescue cell(s) and begins preparation for rescue No rescue cell acquires MS before the acquire timer expires. BSC releases rescue cells

11. Rescue Channel Timeline (rescue scenario: rescue aborted – link restored) MS enables transmitter MS cancel rescue allowed timer, enables transmitter, and sends PSMM w/o rescue flag set Closed loop power control stops MS Events/Actions Frame errors begin Rescue delay timer Rescue allowed timer 12 bad frames … ... Call continues … ... 2 good frames from active set 8 bad frames Rescue acquire timer BSC Events with Sample Actions Rescue cell(s) finger acquires MS and enables transmitter, but no PSMM w/rescue flag set, so BSC releases rescue cells Rescue cells begin listening to MS waiting to lock a finger on MS BSC selects rescue cell(s) and begins preparation for rescue