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This tutorial section on LTE basics covers following sub topics:
Main page  features  terminologies  Frame  TDD FDD  Channel types  PHY  stack  throughput  VoLTE  CA   cell search  network entry  Timers  PSS vs SSS  Security   LTE Bands  EARFCN  Hotspot  router 


This tutorial on LTE covers LTE channels.

LTE technology works based on three channel types viz. logical channel,transport channel and physical channels. These channels are used by lower layers to provide services to the upper layers.

The access points to the Layer L2/L3 are transport channels. They get mapped to physical channels. These physical channels will have different modulation-code rate as mentioned below and are exclusively used by LTE PHYSICAL Layer to carry upper layer information.

LTE Logical,Transport and Physical channels

Following figure mentions LTE logical channels,transport channels and physical channels and mapping between them.

LTE logical transport physical channels mapping

As shown logical channels are of two types; one carrying control information and the other carrying traffic informtion. These gets mapped to transport channels as depicted in the figure. The left side is downlink channel mapping and right side is uplink channel mapping.

Physical Channels

PDSCH - Stands for Physical Downlink Shared Channel, mainly used to carry high speed data/multimedia information. Can be either QPSK/16QAM/64QAM.

PDCCH - Stands for Physical Downlink Control Channel, mainly used to carry UE specific control information. It will have QPSK modulation used.It is mapped on resource elements(REs) in first 3 OFDM syms(symbols) in first slot of subframe.

CCPCH - Stands for Common Control Physical Channel, carries cell-wide control information. QPSK is used. CCPCH is transmitted exclusively on 72 subcarriers centered around DC carrier.

Physical Signals

Physical signals do not convey L2/L3 layer information, but mainly used for synchronization and channel estimation purpose. RS is used for estimating channel response. P-SS and S-SS synchronization signals used for determining network frame timing information i.e. start of the information.

Transport Channels

• Downlink and Uplink transport channels carry L2/L3 information.
• It also configures LTE PHY layer.
• It sends status information such as packet error and CQI to upper layers.
• Also supports peer-peer signaling between higher layers.

Based on broadcast,unicast or multicast concept different transport channels exist. Downlink channels include BCH(broadcast channel),DL-SCH(downlink shared channel, to multiple mobile subscribers or UEs),PCH(paging channel, used for UE DRX and broadcasted over entire cell ),MCH(multicast channel, transmitted over entire cell). Uplink channels include RACH(Random Access Channel), UL-SCH(Uplink Shared Channel).

Uplink PRBs(Physical Resource Blocks) are assigned to UE by eNodeB scheduler. PUSCH is used and shared by multiple UEs to carry upper layer information towards eNodeB. It will employ QPSK/16QAM/64QAM modulation types.

LTE channels

LTE PSS SSS
LTE RS DMRS SRS
LTE PUSCH
LTE PUCCH
LTE PRACH
LTE PMCH
LTE PHICH
LTE PDSCH
LTE PDCCH
LTE PCFICH
LTE PBCH

               

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