Random Access Procedure (RACH) - 4G LTE

Random access (RA) is a basic procedure for uplink synchronization between UE & Network and enables uplink transmission.

RA procedure can occur at various scenarios such as :-

a. Initial Access -
UE connects to NW first time
UE synchronize with NW (RRC Idle)

b. Mobility -
UE moves from one cell to another

c. Connected -
UE synchronize with NW (RRC connected)
UE will be allocated resources in UL

d. UE positioning
UE positioning using Timing Advance

Mapping of RA resources:-
In the frequency domain, a PRACH transmission has a bandwidth of six resource blocks. PRACH frequency offset defines location in frequency domain.

In the time domain, the transmission is usually one subframe long, but it can be longer or shorter. PRACH configuration index defines allowed system frame and subframe numbers for random access attempts, and the preamble format.

*** 👉 This lecture belongs to RAN Engineering course and to learn more about it, please refer to the complete course at - https://www.itelcotech.com/learningpath/ran-engineer-4g-and-5g