eNodeB is the RAN node in the EPS architecture that is responsible for radio transmission and reception from UEs in one or more cells.The eNode B is connected to Core Network nodes by means of an S1 interface. The eNodeB may also be connected to its neighbor eNdoeBs by means of the X2 interface.
The list below describes main functionalities provided by eNodeB.
Cell control and MME pool support: eNodeB owns and controls the radio resources of its own cells. Cell resources are requested by and granted to MMEs in an ordered fashion. This arrangement supports the MME pooling concept. S-GW pooling is managed by the MMEs and is not really seen in the eNodeB.
Mobility control :The eNodeB is responsible for controlling the mobility for terminals in an active state. This is done by ordering the UE to perform measurement and then performing handover when necessary.
Control and User Plane security : The ciphering of user plane data over the radio interface is terminated in the eNodeB. Also the ciphering and integrity protection of RRC signaling is terminated in the eNodeB.
Shared Channel handling : Since eNode B owns the cell resources, eNodeB also handles the shared and random access channels used for signaling and initial access.
Segmentation/Concatenation: Radio Link Control (RLC) Service Data Units (SDUs) received from the Packet Data convergence Protocol (PDCP) layer in the SGW consists of whole IP packets. These IP packets may be larger than the transport block size provided by the physical layer. Thus, the RLC layer must support segmentation and concatenation to adapt the payload to the transport block size.
Hybrid Automatic Repeat Request (HARQ) : MAC layer with fast feedback provides a means for quickly correcting most errors from the radio channel. To achieve low delay and efficient use of radio resources, the HARQ operates with a native error rate which is sufficient only for services with moderate error rate requirements such as for instance VoIP. Lower error rates are achieved by letting an outer Automatic Repeat Request (ARQ) layer in the eNodeB handle the HARQ errors.
Scheduling : A scheduler with support for the QoS model provides efficient scheduling of User Plane (UP) and control plane (CP) data.
Multiplexing and Mapping : The eNodeB performs mapping of logical channels onto transport channels.
Physical layer functionality : The eNodeB handles the physical layer such as scrambling, Transmission diversity, beam forming processing, and OFDM modulation. The eNodeB also handles Layer 1 functions like link adaptation and power control.
Measurements and reporting: eNodeB provides functions for configuring and making measurements on the radio environment and eNodeB-internal variables and conditions. The collected data is used internally for radio resource management ( RRM ) but can be reported for the purpose of multi-cell RRM.