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:

A more detailed view:

Channels

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

Downlink

Channels used by the eNodeB:

Uplink

Channels used by the UE:

Downlink Data Flow

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

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:

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

Transmission Modes

Acronyms

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.

References

• Understanding LTE with Matlab (source of most figures)