1. HRPD System Time in LTE tunneled mode
May Osaka, Japan
HRPD System Time in LTE tunneled mode
Sources:
Jialin zou
Ericsson
Octavio Lima
Motorola
Javed Khan
Ke-Chi Jang
Verizon
Zheng Zhao
VIA
Tony Lee
Recommendation:
Adopt as part of the stage 2 for C.S0087
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2. Overview Normal Initialization State Protocol (ISP) operation
InitializationState.Activate (from ALMP) triggers the activation of the ISP and the AT goes to the Network Determination State
After the HRPD network is selected, the AT enters the Pilot Acquisition State
After the pilot is acquired, the AT enters the Synchronization State
AELMNV single receiver ISP proposal provided mechanism on how the single receiver AT transition through the ISP when in tunnel mode
Two HRPD system time mechanism were agreed by 3GPP LTE
49-bit system time for async mode
39-bit system time for sync mode (i.e. sync with CDMA)
LTE reference: R /R

3. Timing Synchronization consideration
Synchronization State – Timing Synchronization procedures for AT when in tunneling mode
Disable the ISPSyncAcq timer
Set default value for MaximumRevision (max value) and MinimumRevision (0x00)
Define system time acquisition procedure for tunneling mode
Specify that the CDMA system time value in SIB-8 is based on zero offset Pilot PN sequence
Interpret CDMA system time value in SIB-8 according to LTE system time definition (both sync mode and async mode)
Determine CDMA system time at mobile based on the acquired HRPD pilot
For Single Rx terminals, this will only occur when measurement gaps permit (active) or DRX periods permit (idle)
For Dual Rx terminals, this may occur when measurement control indicates (active) or CDMA neighbors are broadcast in SIB8 (idle)
Return a NetworkAcquired indication when CDMA system time at mobile is determined
ISP then enter the Inactive State

4. System Time – Async mode
In Async mode, the LTE system timing is independent to CDMA time. The system time resolution is determined from the following factors:
The HRPD system time stamp: 37 bits in unit of 26.66…ms, i.e CDMA chips
After a CDMA pilot is acquired, its PN offset shall be resolved at the AT. The PN offset of closest CDMA neighbor pilots is 64 chips
The resolution of the CDMA system time determines the resolution of the search window position, and the inaccuracy of the search window position leads to ambiguity when resolve the PN offset
To reduce the chance of ambiguity of resolving PN offset, the resolution of system time is decided to be 1/8 of 64 chip = 8 chips, therefore, the number of the bits of CDMA system time = 49 bits
The 36-bit 1x system time stamp in unit 80ms can also be derived from the 49-bit system time

5. System Time – Sync mode concept
CDMA HRPD system time is a 37-bit field in unit of ms (frame)
The time that can be represented is years based on 01/01/1980 start date
1XRTT system time (based on std)
system time field is 36-bit long with unit of 80ms (one super frame)
So, 2^36 x 0.08 / 3600 / 24 / 365 = Year (from 1980)
Sync Mode: – where LTE frames 10ms frames are aligned with CDMA System time
Instead of 49-bits for aysnc mode, HRPD system time can be reduced to 39 bits when transmit over LTE using SIB-8 with increments of 10ms, where
2^39 x 0.01 / 3600 / 24 / 365 = Year

6. SIB8 System Time Definition
Two system time options controlled by EUTRA Synchronization indicator
If the indicator is set to “true”, the LTE system time is synchronized to CDMA system time
39-bit system time field is used based on 10ms (SFN) timing unit
The system time corresponding to the SFN boundary at or after the ending boundary of the SI-Window (where SIB8 is transmitted)
If the indicator is set to “false”, the system time is Async mode
49-bit system time field is used
The timing unit is 8chips
The system time corresponding to the SFN boundary at or after the ending boundary of the SI-Window
The system time specified in SIB8 is based on the zero offset Pilot PN Sequence