Radio Interface Structure of LTE

The radio interface is structured in a layered model, similar to WCDMA, with a layer 2 bearer (here called EPS Bearer Service), which corresponds to a PDP-context in Rel. 6, carrying layer 3 data and the end-to-end service. The EPS bearer is carried by the EUTRA Radio Bearer Service in the radio interface. The E-UTRA radio bearer is carried by the radio channels. The radio channel structure is divided into logical, transport and physical channels. The logical channels are carried by transport channels, which in
turn are carried by the physical channels as illustrated in Figure.

The protocols performing the functions in the radio interface are:


PDCP (Packet Data Convergence Protocol), RLC (Radio Link Protocol), MAC (Medium Access Control) and the physical layer. For control signaling the RRC (Radio Resource Control) protocol
is used to transfer the NAS (Non Access Stratum) information over the radio interface.


The PDCP protocol maps the EPS bearer onto the E-UTRA Radio Bearer and performs Robust Header Compression (ROHC). The RLC protocol maps the E-UTRA Radio Bearer to a logical channel and performs segmentation, in-sequence delivery and retransmissions. The MAC protocol maps the logical channel to a transport channel and is responsible for Hybrid ARQ (HARQ) and scheduling. The physical layer maps the transport channel onto a physical channel and performs channel coding, modulation etc.