LTE Internals

Daniel Weibel
Created 14 Jul 2016
Last updated 5 Aug 2016

Internal workings of LTE, with special focus on Layer 1 (PHY) and Layer 2 (MAC).

For a list of acronyms, see Acronyms.

Protocol Architecture

The layers of the LTE protocol:

Protocol Architecture 1

A more detailed view:

Protocol Architecture 2


A channel can be seen like a “category” of a piece of data that is passed between protocol layers (and exchanged between network entities).

Channels used by the eNodeB:

Downlink Channels

Channels used by the UE:

Uplink Channels

Downlink Data Flow

Flow of data packages that an eNodeB sends to an UE:

Downlink Data Flow

DL-SCH Processing in the PHY Layer

This shows what happens when the MAC layer on the eNodeB passes some data to the PHY layer on the DL-SCH channel:

DL-SCH Processing 2

The following shows the same as the above figure, but illustrated differently:

DL-SCH Processing 1

Transmission Modes

Transmission Modes


The following is a list of acronyms that are used in this document:

LTE Long-Term Evolution
UE User Equipment
MME Mobility Management Entity
NAS Non-Access-Stratum
RRC Radio Resource Control
PDCP Packet Data Convergence Protocol
RLC Radio Link Control
MAC Medium Access Control
PHY Physical
CRC Cyclic Redundancy Check
HARQ Hybrid Automatic Repeat Request
OFDM Orthogonal Frequency-Division Multiplexing

The acronyms of the channels are resolved directly in the figures of the downlink and uplink channels.