What are the functionality of eNodeB?

E-UTRAN consists solely of the evolved Node B (eNB), which is responsible for all radio interface functionality.


eNB is the RAN node in the EPS architecture that is responsible for radio transmission to and reception from UEs in one or more cells. The eNB is connected to EPC nodes by means of an S1 interface.The eNB is also connected to its neighbor eNBs by means of the X2 interface. Some significant changes have been made to the eNB functional allocation compared to UTRAN. Most Rel-6 RNC functionality has been moved to the E-UTRAN eNB. Below follows a description of the functionality provided by eNB.


1. Cell control and MME pool support


eNB 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 eNB.


2. Mobility control


The eNB is responsible for controlling the mobility for terminals in active state. This is done by ordering the UE to perform measurement and then performing handover when necessary.


3. Control and User Plane security


The ciphering of user plane data over the radio interface is terminated in the eNB. Also the ciphering and integrity protection of RRC signaling is terminated in the eNB.

4. Shared Channel handling


Since the eNB owns the cell resources, the eNB also handles the shared and random access channels used for signaling and initial access.


5. Segmentation/Concatenation


Radio Link Control (RLC) Service Data Units (SDUs) received from the Packet Data Convergence Protocol (PDCP) layer consist of whole IP packets and 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.


6. HARQ
A Medium Access Control (MAC) Hybrid Automatic Repeat reQuest (HARQ) 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 eNB handle the HARQ errors. 


7. Scheduling


A scheduling with support for QoS provides for efficient scheduling of UP and CP data. 


8. Multiplexing and Mapping


The eNB performs mapping of logical channels onto transport channels.


9. Physical layer functionality


The eNB handles the physical layer such as scrambling, Tx diversity, beamforming processing and OFDM modulation. The eNB also handles layer one functions like link adaptation and power control.


10. Measurements and reporting


eNB provides functions for configuring and making measurements on the radio environment and eNB-internal variables and conditions. The collected data is used internally for RRM but can be reported for the purpose of multi-cell RRM.