Subject: Date:
LTE Timing Advance 10/29/2010
Some information related to Timing Advance in LTE (RL10) Basics
L1 Procedures & eNB measurements PHY Layer Procedures
Timing 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 Confidential 4 © Nokia Siemens Networks
LTE RL1/CH_4 (SFS BLSv8.3) / Peter Stöckl / January 2010
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
Continuous Timing Advance
11-bit TA command with
6-bit TA command with
TA= 0, 1, 2, …, 1282
TA= 0, 1, 2, …, 63
NTA = TA x 16
NTA,NEW = NTA,OLD + (TA - 31) x 16
Therefore TA granularity = 16 x 32.552ns ≈ 0.52µs
Therefore pos/neg. adjustment in steps of 0.52µs
(TA = 2* propagation delay resolution ≈ 156m/2) Confidential 5 © Nokia Siemens Networks
LTE RL1/CH_4 (SFS BLSv8.3) / Peter Stöckl / January 2010
Peter Stöckl NWS LTE RA E2E SA NE LTE&Access
Page 1 of 7
Subject: Date:
LTE Timing Advance 10/29/2010
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; o clear any configured downlink assignments and uplink grants.
Peter Stöckl NWS LTE RA E2E SA NE LTE&Access
Page 2 of 7
Subject: Date:
LTE Timing Advance 10/29/2010
Involved Parameters Abbreviated Name
taTimer
Parameter Id MO Class Parameter relationships
53557 LNCEL taTimerMargin must be less or equal than (taTimer-10ms)
Short description
Determines the number of subframes after which a UE assumes it is outof-sync in UL if no Time Alignment command was received.
Description
Determines the number of subframes after which a UE assumes it is outof-sync in UL if no Time Alignment command was received.
Full name
Time Alignment timer
3GPP Name Range and Step
timeAlignmentTimer 500 (0), 750 (1), 1280 (2), 1920 (3), 2560 (4), 5120 (5), 10240 (6)
Default value Default value notes Hidden Internal value Modification
1280 (2)
Abbreviated Name
taMaxOffset
Parameter Id MO Class Parameter relationships
53556 LNCEL
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 Range and Step
0...5 us, step 0.01 us
BTS restart needed
Peter Stöckl NWS LTE RA E2E SA NE LTE&Access
Page 3 of 7
Subject: Date:
LTE Timing Advance 10/29/2010
Default value Default value notes Hidden Internal value Modification
0.52 us Corresponds to 16*Ts
Abbreviated Name
taTimerMargin
Parameter Id MO Class Parameter relationships
65249 LNCEL 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
internal_value = gui_value * 100 Requires object locking
Default value Default value notes Hidden Internal value Modification
89 subframes
Abbreviated Name
taCmdMaxRetry
Parameter Id MO Class Parameter relationships
53117 LNBTS
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.
internal_value = gui_value Not modifiable
Peter Stöckl NWS LTE RA E2E SA NE LTE&Access
Page 4 of 7
Subject: Date:
LTE Timing Advance 10/29/2010
Full name
Maximum number of time alignment command retries
3GPP Name Range and Step
1...10, step 1
Default value Default value notes Hidden Internal value Modification
1
Abbreviated Name
taOffScheMarg
Parameter Id MO Class Parameter relationships
53118 LNBTS
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 Default value notes Hidden Internal value Modification
Yes internal_value = gui_value Not modifiable
2 us Yes internal_value = gui_value * 10 Not modifiable
Peter Stöckl NWS LTE RA E2E SA NE LTE&Access
Page 5 of 7
Subject: Date:
LTE Timing Advance 10/29/2010
Maintenance of Uplink Time Alignment (according SFS) (in figures)
Peter Stöckl NWS LTE RA E2E SA NE LTE&Access
Page 6 of 7
Subject: Date:
LTE Timing Advance 10/29/2010
Maintenance of Uplink Time Alignment (according SFS) (in bullets) •
UL TA update shall be done o Periodically o On per-need basis
•
Timing Alignment Timer shall be started/restarted whenever an initial TA or TA update command is received. (Exception: see 3GPP block above)
•
If timer expires UE detects out-of-sync status
•
Interval between periodic TA update commands is calculated as taTimer - taTimerMargin
•
Per-need-TA update is required if reported time alignment offset > taMaxOffset
•
If reported time alignment offset > taSchedulingThreshold then UL scheduler is informed that UE is drifting out of alignment taSchedulingThreshold = max(taOffScheMarg; taMaxOffset + 0.5μs)
•
HARQ ACK feedback is received for TA command For a per-need TA command and when taSchedulingThreshold was exceeded inform UL scheduler that the TA is OK again The periodic timing alignment timer is (re)started
•
NO HARQ ACK feedback is received for a TA command within max number of DL HARQ transmissions TA update command shall be repeated up to taCmdMaxRetry or until the timing alignment timer expires If maximum number of retries is exceeded or the timing alignment timer has expired, then status UE UL out-of-sync id detected.
Peter Stöckl NWS LTE RA E2E SA NE LTE&Access
Page 7 of 7
