ible preambles lead to successfully decoded message 3. It should be noted that message 3 HARQ retransmissions are typically non-adaptive HARQ retransmissions (to save the PDCCH capacity) which means that all message 3 retransmissions use exactly the same resources (number of PRBs, PRB location, MCS and transport block size) as the initial transmission and therefore there is no frequency-selective scheduling gain between the initial transmission and HARQ retransmissions. Figure 12.11 shows an example of cell suffering from high level of uplink interference and how RACH success rate gets impacted by it. As mentioned above, the eNodeB impacts on message 3 transmission power based on the parameters DeltaPreambleMsg3 and Amsg2 but it is not recommended to maximize the UE transmission power for message 3 to maximize the RACH success rate due to the increased inter-cell interference which would then degrade the performance during high traffic (as shown in Figure 12.11). It is better to optimize message 3 capacity grant parameters such as the number of used PRBs, which is defined based on the size of message 3 and therefore depends also on the terminal selected preamble group, and MCS together with the transmission power parameters. It should be noted that minimum amount of bits that should LTE Key Performance Indicator Optimization Average PUSCH Random access setup success rate Figure 12.11 Random access setup success rate and PUSCH signal to interference and noise ratio in a cell be assigned to message 3 is 56, which is large enough for RRC connection request message. Figure 12.12 shows improvement in RACH success rate by optimized uplink grant parameters and transmission power parameters for message 3. It should be noted that optimization of uplink grant was started in day 16 and finished on day 45. The improvement after day 45 is explained later in Section 12.4.2. With physical layer optimization, it is possible to reduce the total amount of preambles the eNodeB receives. The random access setup success rate is impro