Hi Expert,
I need clarification on Timing Advance (TA) and Timing Offset.
When the UE sends an RRC CONNECTION REQUEST, it may have different timing offsets such as 2, 4, 9, 10, 14, or 17.
What do these values indicate?
Does this mean the UE is sending Msg3 from a farther distance?
Could you please explain how these offsets impact the transmission timing?
It could be a Backoff Timer, which is provided in the RAR (Random Access Response) as a 4-bit value.
If the UE does not receive Msg2 or if Msg4 is not intended for it, the UE will retry after the backoff time. The backoff time is a random value, constrained by the maximum backoff timer value set in the RAR (Random Access Response) message.
Msg2 (RAR) is received correctly, and that’s fine.
My concern is about the RRC Connection Establishment process, which includes RRC CONNECTION REQUEST, RRC CONNECTION SETUP, and RRC CONNECTION COMPLETE.
Different timing offsets represent the backoff time.
Values like 2, 4, 9, 10, 14, and 17 indicate the backoff time durations.
Thanks for your proactive response.
My query is related to the process after Msg2 (RAR) is successfully received. After that, the UE sends Msg3 (RRC CONNECTION REQUEST) to the eNodeB with Timing Advance. The eNodeB then applies an internal algorithm to determine the Timing Offset.
This is where my confusion lies - how exactly does the eNodeB calculate the timing offset?
I am considering Preamble as Msg1 and RAR as Msg2.
The Backoff Timer applies to Msg1 initiation, so I believe I may not have fully understood your question correctly.
The Backoff Time applies to the RACH process.
My concern is about the RRC Connection Establishment KPI after the RACH procedure, when the UE initiates the RRC CONNECTION ESTABLISHMENT process.
If two mobiles use different preambles, the gNB will assign different TA values to each.
However, if both mobiles use the same preamble, they will receive the same TA in the RAR message, regardless of their different locations within the cell.
This TA is then used by the UE when sending the RRC Connection Request.
Okay, TA (Timing Advance) and timing offset both represent the distance between the UE and the eNodeB, but TA is a quantized value used for uplink timing alignment?
I’m not familiar with the term “timing offset,” but I do know that TA (Timing Advance) is included in the RAR message.
As per my understanding Timing Advance is that when the UE sends a Random Access Request in Message 1, different UEs might use the same common preamble signature.
In Message 2 (RAR Response), the network follows a first-come, first-served approach to allocate the preamble.
Right?
Timing Advance will be used by the UE for sending the RRC Connection Request.
This is RAR:
The mobile will calculate Timing Advance (TA) using the following formula:
Timing offset for the UE is the time delta between the borders of DL subframes and borders of UL subframes from UE perspective and it is typically negative. The value is sent to the UE from eNodeB as Timing Advance value using TA command
During CBRA, an absolute value is sent by eNB is RAR based on preamble delay in msg1.
To maintain UL synchronization, eNB needs to regularly send other TA commands with relative TA value with respect with previous TA
If UE doesn’t get TA until TAtimer expiry, UE has to intiatw another CBRA
