LTE Terms

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• LTE Terminology

LTE Terminology

This page on LTE terminology covers LTE and LTE advanced technology related terms.

eNB or eNodeB It is similar to Base station which is used in GSM networks. Also called as eNodeB.

UE: It is similar to mobile subscriber.

OFDMA: Orthogonal Frequency Division Multiple Access, used in physical layer of LTE Downlink.

SC-FDMA: Single Carrier Frequency Division Multiple Access, used in physical layer of LTE Uplink.

LTE Frame: LTE frame are of 2 types TDD and FDD. In both the cases, frame is composed of 10 sub frames and each sub frame is made of 2 slots. Frame size is 10ms.

Resource Block (RB): It is the smallest block of resource that can be allocated to UE by eNB; it is 12 subcarriers for 7 symbols.

Resource Element (RE): The smallest unit of radio resources, one subcarrier for one symbol.

Slot: 7 consecutive symbols for short Cyclic Prefix, 6 symbols for long cyclic prefix.

Sub frame: 2 consecutive timeslots.

Reference Signal: Similar to pilot carrier and is used for channel estimation at the receiver.

Synchronization signal: There are two synchronization signals, Primary and secondary. Both are transmitted in slot 0 and slot 10 in all the frames. It is same as preamble used in earlier systems and used for time, frequency synchronization purpose.

S-GW: Serving Gateway

MME: Mobility Management Entity

X2 interface: Interface used between eNodeB and eNodeB.

S1 interface: Interface used between eNodeB and core network interface (MME/S-GW).

Uu interface: This is the air interface used between eNodeB and UE.

Control channel: This channel carry control information used to make, maintain and terminate the connection. Used for the transfer of control plane information in LTE.

Data channel: This channel carry traffic information. Used for the transfer of user plane information.

Channel structure in LTE: LTE adopts a hierarchical channel structure. LTE defined three channel types i.e. logical,transport and physical channels. Each associats with a service access point (SAP). (SAP) between different layers. These channels are used by lower layers to provide services to the upper layers.

Logical Channels: What to Transmit. They are used by MAC layer to provide services to RLC layer. Each logical channel is defined as per type of information it carries. In LTE, there are two categories of logical channels depending on the service they provide: control channels and traffic channels.

Transport Channels: How to Transmit. PHY uses transport channel to offer services to the MAC layer. It is characterized by how and with what characteristics data is transferred over the air.

Physical Channels: Actual transmission Each physical channel maps to a set of resource elements in the time frequency grid that carry information from upper layers. The basic entities that make a physical channel are REs and RBs. A resource element is one subcarrier by one OFDM symbol and typically this could carry one (or two with spatial multiplexing) modulated symbol(s). A resource block is a collection of resource elements and in the frequency domain this represents the smallest quanta of resources that can be allocated.

P-SS: Primary synchronization signal

S-SS: secondary synchronization signal

PBCH: Physical Broadcast Channel

PDSCH: Physical Downlink Shared Channel

PDCCH: Physical Downlink Control Channel

PCFICH: Physical Control Format Indicator Channel

PHICH: Physical Hybrid ARQ Indication Channel

PCH: Paging channel

RS: Reference Signal, used both in uplink and downlink

SRS: Sounding reference signal, used in uplink

DMRS: Demodulation Reference Signal

PRACH: Physical Random Access Channel used in uplink

PUSCH: Physical Uplink Shared Channel

PUCCH: Physical Uplink Control Channel