4G5GWorld has a new home now. Visit TelecomGrid for new stories and blogs!
Timing Advance Command
Posted on 30. Jun, 2013 by gcc
in LteWorld Forum
============================================================================
Timing Advance is a MACi CE that is used to control Uplinki signal transmission timing. Network (eNodeBi in this case) keep measuring the time difference between PUSCH/PUCCH/SRS reception and the subframe time and can send a 'Timing Advance' command to UEi to change the PUSCH/PUCCH transmission to make it better aligned with the subframe timing at the network side. If PUSCH/PUCCH/SRS arrives at the network too early, network send a Timing Advance command to UE saying "Transmit your signal a little bit late", If PUSCH/PUCCH/SRS arrives at the network too late, network send a Timing Advance command to UE saying "Transmit your signal a little bit early".
MAC PDUi for Timing Advance is as follows. It is one byte data and the first two bits are reserved and set to be always 0. The remaining 6 bits carries Timing Advance command value ranging from 0 to 63.
============================================================================
I READ ABOVE IN LTEi SPEC AND FROM INTERNET.
My doubt is that in which "msg" from eNodeB to UE, Timing advance command is sent?
I am using wireshark FAPI logs to understand this and so far i have seen "Timing advance" calculation for ULSCH,RACH,SRS and CQI pdu's(Received at eNodeB side). When and HOW eNodeB send "Timing advance Command" to UE based on "Timing advance calulation" so that UE could adjust its uplink signal timings???
Did you check
Did you check http://lteworld.org/blog/timing-advance-ta-lte
Timing Advance Command is sent in Random Access Response (MACi PDUi), also part of MAC PDU for DL-SCH (indicated by MAC header)
Timing Advance
I have seen one parameter "timing advance" in following PDUi's received by eNodeBi from UEi
ULSCH.indication(FAPI MsgId 0x87) for received UL PDU,
RACH.indication (FAPI MsgId0x88) for received preamble
SRS.indication (FAPI MsgId 0x89) for SRS pdu
Want to verify my understanding:-
1. "Timing advance" is computed for above mentioned PDU's at PHY layer on their arrival from UE ?? YES/NO
2. "Timing Advance Command" under MACi PDU HEADER lcid 11101 is sent to UE based on computed Timing advance?? YES/NO
3. Size of "Timing advance" and "Timing advance Command" pdu is 1 Byte?? YES/NO
For first probably yes, can
For first probably yes, can not comment on msgid
2) LCID 11101 (Timing Advance Command)in DL SCH MACi PDUi
3) In case of random access response, 11-bit timing advance command; In other cases (MAC PDU), 6-bit timing advance command
Timing Advance
How to calculate the relative distance from UEi to eNodeBi with the TA value
3GPPi 36.213: Upon reception
3GPPi 36.213: Upon reception of a timing advance command, the UEi shall adjust its uplink transmission timing for PUCCH/PUSCH/SRS. The timing advance command indicates the change of the uplink timing relative to the current uplink timing as multiples of 16*Ts. (~0.52 micro sec).
You know the radio wave speed, can get the distance.