3
Radio Interface Signaling Procedures
As described in Chapter 1, one of the major changes along the evolutionary path from 3G UMTS to LTE is the fact that eNodeBs host the radio resource management functions while in 3G UMTS all radio resources (frequencies, codes, power thresholds) have been controlled by the RNC. To implement the radio resource management in the eNodeB results in turn in the fact that also the protocol entity used to negotiate the usage of radio resources between the User Equipment (UE) and network must be part of the eNodeB software. Hence, the Radio Resource Control (RRC) protocol terminates on the network side in the eNodeB. From this it emerges that the eNodeB not only is responsible for setting up and releasing RRC connections and the radio bearer, but must also handle all RRC measurement tasks and resulting handover decisions. Thus, the most interesting and most crucial parameters for radio network optimization in LTE networks are found and can be tuned in the eNodeB.
Looking at the LTE RRC protocol itself as described in 3GPP 36.331, at first sight most of the message names sound familiar or are even identical to what was described in 3GPP 25.331, the RRC protocol standard for 3G UMTS. But significant differences emerge when going into detail and checking the meaning of particular information elements as well as the interaction of the RRC protocol with the underlying Medium Access Control (MAC) transport layer and the upper level Non-Access Stratum (NAS) ...
