Overview of LTEPhysical layer

Service Goals

•Data transfer rate ( max)DL: 150Mbps, UL: 50Mbps•Mobility : 0-15 km/h best performance 15-120 km/h high performance

Physical Layer Details

• Modulation scheme : DL: OFDMA/ UL : SC-FDMA•Duplex Modes : FDD, TDD• Frequency bands : 800 MHz, 900 MHz, 1800 MHz, 2000 MHz, 2600MHz •Channel bandwidths FDD: 1.4, 3, 5, 10, 15, 20 MHz•DL transmission OFDM using QPSK, 16QAM, 64QAM•UL transmission SC-FDMA using QPSK, 16QAM ,64QAM•Number of carriers72 to 1200•Carrier spacing Fixed 15 kHz (7.5 kHz extended CP)•Additional mod types Zadaoff-Chu, BPSK

OFDMA SC-FDMA

OFDMA : High spectral bandwidth efficiency, robustness to frequency selective fading channels, etc.

Frame Structure (FDD)

Symbol Structure

Resource Block (RB) :Smallest unit used by the scheduling algorithm

LTE Radio interface

Physical signals Physical channels

• Physical signals are generated purely in physical layer and used for system synchronization, cell identification, and radio channel estimation.

• Physical channels carry data from higher layers including control, scheduling, and user payload.

Physical Layer channels

Physical signal

Primary synchronization signal

Secondary synchronization signal Reference signal

Used for cell search and identification by the UE. Carries part of the cell ID (one of three orthogonal sequences

Used for cell search and identification by the UE.Carries the remainder of the cell ID (one of168 binary sequences)

Used for downlink channel estimation.(Receiver to estimate the amplitude and phase flatness of the received signal)

PBCH

PMCH

PDCCH

PDSCH

PCFICH

Carries cell-specific system information

Carrying RB allocation information, modulation and coding scheme used for DL user data, power control information

Payload

To indicate how many OFDMA symbols are reserved for control information. This can vary between one and three the for each 1ms SF.

PRACH

PUCCH

PUSCH

Call setup

Scheduling Request, Channel Quality Information, ACK/NACK

Payload

DLU

L

PHICHTo indicate in the downlink whether an uplink packet was correctly received or not.

Carries the MCH transport channel for requirement to be broadcast in the entire coverage of the cell

PCCH DTCH BCCHDCCHCCCH MCCH MTCH

PCFICH PDCCH PBCH PHICH PMCHPDSCH

PCH DL-SCH BCH MCH

Trt

Log

Phy

• The PSS is mapped in the last symbol of slot #0 and slot #10

• The SSS is allocated in the symbol just before the PSS.

• The RSs are located at symbol #0 and symbol #4 of every slot (The reference signal takes precedence over any other allocation)

• The PBCH is mapped to the first four symbols in slot #1.

•The PDCCH can be allocated to the first three symbols.

•The remaining unallocated areas can be used for the PDSCH