3G/UMTS

  

 

 

 

PRACH Power

 

Initial PRACH (The first PRACH that UE transmit) is determined by the following formula.

 

Initial RACH Preamble Power = Primary CPICH TX Power – CPICH_RSCP + UL_Interference + Constant Value

 

CPICH_RSCP is the power directly measured by UE and all other parameters are calculated (obtained) from system information. The related parameter and system information is as follows.

 

System Information

Information Element

Example Value

SIB3

Maximum Allowed UL Tx Power

21 dBm

SIB5

Primary CPICH Power

-8 dBm

Power Ramp Step

3 dB

Mmax

2

NB01min

10

NB02max

10

SIB7

UL Interference

-92

 

If UE fail to get AICH for the PRACH, it increment the PRACH power by Power Ramp Step (SIB5) and transmit the PRACH again. UE repeat this process until it gets AICH or it retried the specific number specified in SIB5.

Following screenshot is an example of PRACH transmission and retransmission. This is from a test resultl of 34.121 8.4.2.1. In this test case, Network intentionally does not send AICH so that UE keep sending PRACH with specified power increment in the specified number of times.