What is the TA for RACH request message to send?

Question

Handover RACH will be initiated as Contention free, RNTI will be included in Mobility info. But while doing RACH What will be the RNTI value included in RAR? Will this be same as Mobility RNTI?

Answer 1

Timing advance is a special command that is triggered by an eNodeB towards an UE to adjust the uplink transmission. In particular RACH case, UE uses physical RACH (PRACH) channel to send preamble request. After receiving either eNodeB grants uplink resources or it ask UE to re-try after some amount of time (timing advance).
For the other uplink transmissions through PUCCH/PUSCH/SRS channels, eNodeB may ask UE to adjust its transmission time (either to send a bit early or a bit late). EnodeB calculates value of timing advance based on the sub frame timing and arrival of uplink arrival.
It informs UE about timing advance by using Timing advance MAC CE. The value of timing advance ranges from 0 to 63 and there is an equation to calculate uplink transmission time.

Comments

Thank you, But what is TA for PRACH ? if no TA then why does this channel doesn't have TA ? Even PRACH is also an channel like other PUSCH then this also should have TA right?