What is the Rach process Why Rach is required?
What is the Rach process Why Rach is required?
RACH is a PHY and MAC layer process, For a UE to initiate RACH it has to get the some information before it can send a RACH to the gNB, UE gets this information from the gNB. It needs Information such as which PRACH preamble to use and When to send PRACH i.e. PRACH occasions.
What is LTE Rach procedure?
LTE random access procedure is used by the UEs to initiate a data transfer. (2) The three UEs initiate the random access procedure at exactly the same time. Two of them (UE-A and UE-B) happen to pick the same preamble. This results in a resulting in a collision.
How contention resolution happens in LTE?
LTE random access procedure is used by the UEs to initiate a data transfer. UE-C picks a distinct preamble so it succeeds in the random access procedure. Contention between UE-A and UE-B is resolved in UE-A’s favor.
What is contention free Rach LTE?
Usually in this case, the Network informs each of the UE of exactly when and which preamble signature it has to use. Of course, in this case Network will allocate these preamble signature so that it would not collide. This kind of RACH process is called “Contention Free” RACH procedure.
What is the channel use to send Rach?
physical random access channel
The UL common physical channels are physical random access channel (PRACH) used to carry the RACH and fast uplink signaling channel (FAUSCH) and physical common packet channel (PCPCH) to carry CPCH.
Which DCI format does RAR LTE use?
DCI Formats which carries scheduling information for RAR are DCI Format 1A and DCI Format 1C in ‘common search space’.
What is prach frequency offset in LTE?
PRACH Frequency Offset
| System Bandwidth | Resource Block Offset Range | Resource Block Offset Default Value |
|---|---|---|
| 5 MHz | 0 to 19 | 0 |
| 10 MHz | 0 to 44 | 0 |
| 15 MHz | 0 to 69 | 0 |
| 20 MHz | 0 to 94 | 0 |
What is contention resolution timer?
Contention resolution timer is to check if the eNB has sent the Contention Resolution Identity MAC CE in response to msg3 to complete the contention resolution procedure (for contention based mechanism). If no such message from eNB during this timer, then the new RACH procedure happened.
What are the functions of random access channel Rach in UMTS?
15.5 Channel Structure in UMTS Terrestrial Radio Access Network
| Channel | Function |
|---|---|
| Random access channel (RACH) | UL channel received over the entire cell, characterized by a limited size data field, a collision risk, and by use of open loop power control |
What is Rach preamble?
A preamble is send by UE to gNB over PRACH channel to obtain the UL synchronization. Similar to LTE, in 5G NR there are 64 preambles defined in each time-frequency PRACH occasion. The preamble consists of two parts cyclic prefix (CP) and Preamble Sequence. Long Preamble.
