Timing Advance

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Subject: LTE Timing Advance Date: 10/29/2010 Peter Stöckl Page 1 of 7 NWS LTE RA E2E SA NE LTE&Access 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 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 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 (N TA + N TA offset ) x T S before the start of the corresponding DL radio frame at the UE T S = 1 / 30.72MHz = 32.552ns N TA offset = 0 for FDD / N TA offset = 624 for TDD / 0 ≤ N TA ≤ 20512 Initial Timing Advance 11-bit TA command with T A = 0, 1, 2, …, 1282 N TA = T A x 16 Therefore TA granularity = 16 x 32.552ns ≈ 0.52µs Continuous Timing Advance 6-bit TA command with T A = 0, 1, 2, …, 63 N TA,NEW = N TA,OLD + (T A - 31) x 16 Therefore pos/neg. adjustment in steps of 0.52μs (TA = 2* propagation delay resolution 156m/2)

description

LTE Timing Advance

Transcript of Timing Advance

Page 1: Timing Advance

Subject: LTE Timing Advance Date: 10/29/2010

Peter Stöckl Page 1 of 7 NWS LTE RA E2E SA NE LTE&Access

Some information related to Timing Advance in LTE (RL10) Basics

4 © Nokia Siemens Networks LTE RL1/CH_4 (SFS BLSv8.3) / Peter Stöckl / January 2010Confidential

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

5 © Nokia Siemens Networks LTE RL1/CH_4 (SFS BLSv8.3) / Peter Stöckl / January 2010Confidential

L1 Procedures & eNB measurements PHY Layer Procedures

Timing Advance

Uplink-Downlink frame timingTransmission 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 UETS = 1 / 30.72MHz = 32.552ns

NTA offset = 0 for FDD / NTA offset = 624 for TDD / 0 ≤ NTA ≤ 20512

Initial Timing Advance11-bit TA command with

TA= 0, 1, 2, …, 1282NTA = TA x 16

Therefore TA granularity = 16 x 32.552ns ≈ 0.52µs

Continuous Timing Advance6-bit TA command with

TA= 0, 1, 2, …, 63NTA,NEW = NTA,OLD + (TA - 31) x 16Therefore pos/neg. adjustment in

steps of 0.52µs

(TA = 2* propagation delay resolution ≈ 156m/2)

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Subject: LTE Timing Advance Date: 10/29/2010

Peter Stöckl Page 2 of 7 NWS LTE RA E2E SA NE LTE&Access

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.

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Subject: LTE Timing Advance Date: 10/29/2010

Peter Stöckl Page 3 of 7 NWS LTE RA E2E SA NE LTE&Access

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 Range and Step 0...5 us, step 0.01 us

Page 4: Timing Advance

Subject: LTE Timing Advance Date: 10/29/2010

Peter Stöckl Page 4 of 7 NWS LTE RA E2E SA NE LTE&Access

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.

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Subject: LTE Timing Advance Date: 10/29/2010

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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

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Subject: LTE Timing Advance Date: 10/29/2010

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Maintenance of Uplink Time Alignment (according SFS)

(in figures)

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Subject: LTE Timing Advance Date: 10/29/2010

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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.