connection attempt is due to the interference which causes increased UE transmission power requirement and therefore higher number of preamble power ramp-up rounds (increased interference causes message 3 reception problems). The preamble power increase for UEs under the cells rejecting the RRC connection setups causes increase in inter-cell interference and therefore reduction in PUSCH SINR for the surrounding cells. This degraded PUSCH SINR in turn causes increase in UE transmission power for the preamble process under the affected cells which in turn causes problems to the surrounding cells due to the increased interference level. Therefore, at the end there is overall decrease in PUSCH SINR across several cells and increase in the number of preambles per RRC connection setup attempt and rapid decrease in random access success rate as shown in Figure 13.20. As explained above the rejected RRC connection setups can cause increase of signalling and therefore increase of inter-cell interference and the impact of RRC connection setup rejections spreads to several cells. Therefore any rejections of RRC connection setups should be avoided and in case of rejections the impact of such rejections should be mitigated as much as possible. The 3GPP-defined t302 timer can be used to delay the RRC connection setup repetitions in case of admission control rejection [8]. However, t302 timer only delays the RRC connection setup re-attempts by t302 time given in RRC connection reject message by eNodeB. Increasing Capacity Optimization Number of preambles per RRC connection setup attempts Figure 13.45 RRC connection setup rejection rate versus number of required preambles per RRC connection setup attempt - only cells and samples for which there are admission control rejections are included the value for t302 to 16 seconds, which is the maximum possible [8], is beneficial during the mass events. Alternatively 3GPP-defined [8] service-specific access class barring can be used to bar the cell for given time. The UE uses the service