RACH = Random Access Channel - Random Access Procedure has to be performed by a User Equipment in 4 situations 1. initial access when in Idle mode 2. handover to a different cell 3. re-establishment of the radio link after radio link failure 4. uplink or downlink data transmission when the UE has no synchronisation on the uplink #### Scenarios when User Equipment is asking for access: 1. **Contention based Random Access Procedure** - Collision when another UE is asking for access at the same time 2. **Contention free / Non-Contention Random Access Procedure** - Network notifies a preamble sequence to the User Equipment to prevent collision. A preamble sequence is a specific pattern which differentiated UEs. ![[Pasted image 20230215130019.png]] ### Value Drivers Optimal RACH performance is essential to obtain **higher coverage** and **lower delays**. Random Access performance is expressed in terms of **Access [[Probability]]** and **Access Delay Probability** - No. of resources allocated to random access has **direct impact on delays**, - Allocating a larger number of resources involves **lower collision probability** ## RACH Optimisation Parameters - resource unit allocation, - preamble split, - back off parameter value - transmission control parameters These parameters can be **different on each cell** and **time variant** There are clear benefits of optimising and self-tuning RACH parameters. #telco