9

Random Access

As described in the previous chapter, the base station explicitly schedules all the transmissions that the mobile carries out on the physical uplink shared channel. If the mobile wishes to transmit on the PUSCH but does not have the resources to do so, then it usually sends a scheduling request on the physical uplink control channel. If it does not have the resources to do that, then it initiates the random access procedure. This can happen in a few different situations, primarily during the establishment of an RRC connection, during a handover, or if the mobile has lost timing synchronization with the base station. The base station can also trigger the random access procedure, if it wishes to transmit to the mobile after a loss of timing ....