Some information related to Timing Advance in LTE (RL10)
Basics
4 © Nokia Siemens Networks LTE RL1/CH_4 (SFS BLSv8.3) / Peter Stöckl / January 2010 Confidential
L1 Procedures & eNB measurements
PHY Layer ProceduresTiming Advance
• Used for alignment of UL/DL sub-frame start at eNB
– eNB shall measure the initial timing advance and perform period update of UL timing correction
– eNB shall send timing advance command to UE
• TA measurements on
– RACH preamble
– Periodic update of UL timing for UE using ▪ Available UL transmission on PUSCH
▪ SRS
▪ Periodic CQI reports on PUCCH
• Two types of TA commands
– Initial TA command 11-bit timing advance command
– Continuous TA measurement 6-bit timing advance command
• Timing adjustment shall apply from sub-frame n+6 in case TA command is received on sub-frame n
5 © Nokia Siemens Networks LTE RL1/CH_4 (SFS BLSv8.3) / Peter Stöckl / January 2010 Confidential
L1 Procedures & eNB measurements
PHY Layer Procedures
Timing Advance
Uplink-Downlink frame timing
Transmission of the UL radio frame from UE shall start at (NTA+ NTA offset) x TS
before the start of the corresponding DL radio frame at the UE TS= 1 / 30.72MHz = 32.552ns
NTA offset= 0 for FDD / NTA offset= 624 for TDD / 0 ≤ NTA≤ 20512 Initial Timing Advance
11-bit TA command with TA= 0, 1, 2, …, 1282
NTA= TAx 16 Therefore TA granularity =
16 x 32.552ns ≈ 0.52µs
Continuous Timing Advance
6-bit TA command with TA= 0, 1, 2, …, 63 NTA,NEW= NTA,OLD+ (TA - 31) x 16 Therefore pos/neg. adjustment in
steps of 0.52µs
Maintenance of Uplink Time Alignment (according to 3GPP)
The UE has a configurable timer timeAlignmentTimer which is used to control how long
the UE is considered uplink time aligned.
The UE shall:
• when a Timing Advance Command MAC control element is received:
o apply the Timing Advance Command;
o start or restart timeAlignmentTimer.
• when a Timing Advance Command is received in a Random Access Response
message:
o if the Random Access Preamble was not selected by UE MAC:
apply the Timing Advance Command;
start or restart timeAlignmentTimer.
o else, if the timeAlignmentTimer is not running:
apply the Timing Advance Command;
start timeAlignmentTimer;
when the contention resolution is considered not successful, stop
timeAlignmentTimer.
o else:
ignore the received Timing Advance Command.
• when timeAlignmentTimer expires:
o flush all HARQ buffers;
o notify RRC to release PUCCH/SRS;
Involved Parameters
Abbreviated Name
taTimer
Parameter Id 53557
MO Class LNCEL
Parameter relationships taTimerMargin must be less or equal than (taTimer-10ms)
Short description Determines the number of subframes after which a UE assumes it is out-of-sync in UL if no Time Alignment command was received.
Description Determines the number of subframes after which a UE assumes it is out-of-sync in UL if no Time Alignment command was received.
Full name Time Alignment timer
3GPP Name timeAlignmentTimer
Range and Step 500 (0), 750 (1), 1280 (2), 1920 (3), 2560 (4), 5120 (5), 10240 (6)
Default value 1280 (2)
Default value notes Hidden
Internal value
Modification BTS restart needed
Abbreviated Name
taMaxOffset
Parameter Id 53556
MO Class LNCEL
Parameter relationships
Short description Determines the maximum allowed Time Alignment offset.
Description Determines the maximum allowed Time Alignment offset. If the value is exceeded, TA command is sent to the UE to adjust UL timing.
Full name Time Alignment maximum offset 3GPP Name
Default value 0.52 us
Default value notes Corresponds to 16*Ts Hidden
Internal value internal_value = gui_value * 100 Modification Requires object locking
Abbreviated Name
taTimerMargin
Parameter Id 65249
MO Class LNCEL
Parameter relationships taTimerMargin must be less or equal than (taTimer - 10ms)
Short description The parameter defines lead with respect to the taTimer expiration time for starting to send the periodic timing advance command.
Description The parameter defines lead with respect to the taTimer expiration time for starting to send the periodic timing advance command.
Full name Time alignment timer margin 3GPP Name
Range and Step 0...2560 subframes, step 1 subframes Default value 89 subframes
Default value notes Hidden
Internal value internal_value = gui_value Modification Not modifiable
Abbreviated Name
taCmdMaxRetry
Parameter Id 53117
MO Class LNBTS
Parameter relationships
Short description The number of times the timing advance command is retried before the LTE MAC assumes the UE has gone out-of-synch.
Description The number of times the timing advance command is retried before the LTE MAC assumes that the UE has gone out-of-synch. This parameter is vendor-specific.
Full name Maximum number of time alignment command retries 3GPP Name
Range and Step 1...10, step 1
Default value 1
Default value notes
Hidden Yes
Internal value internal_value = gui_value Modification Not modifiable
Abbreviated Name
taOffScheMarg
Parameter Id 53118
MO Class LNBTS
Parameter relationships
Short description Determines the time alignment offset limit for the uplink sceduler to stop considering the UE for scheduling.
Description Determines the time alignment offset limit for the uplink scheduler to stop considering the UE for scheduling. This parameter is vendor-specific.
Full name Time alignment offset margin for scheduling 3GPP Name
Range and Step 1.5...4 us, step 0.1 us
Default value 2 us
Default value notes
Hidden Yes
Internal value internal_value = gui_value * 10 Modification Not modifiable
