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Wednesday, 18 January 2012

LTE Physical Layer


LTE Physical Layer:                                                         Reference: 3GPP TS 36.206
  • The Figure below shows the physical layer interfaces the Medium Access Control (MAC) sub-layer of Layer 2 and the Radio Resource Control (RRC) Layer of Layer 3.
  • The physical layer offers a transport channel to MAC.
  • MAC offers different logical channels to the Radio Link Control (RLC)


Service provided to higher layers:

  •    Error detection on the transport channel and indication to higher layers
  •    FEC encoding/decoding of the transport channel
  •    Hybrid ARQ soft-combining
  •    Rate matching of the coded transport channel to physical channels
  •    Mapping of the coded transport channel onto physical channels
  •    Power weighting of physical channels
  •    Modulation and demodulation of physical channels
  •    Frequency and time synchronization
  •    Radio characteristics measurements and indication to higher layers
  •    Multiple Input Multiple Output (MIMO) antenna processing
  •    Transmit Diversity (TX diversity)
  •    Beam-forming
  •    RF processing.


LTE physical signals

Downlink physical signals
Purpose
Primary synchronization signal
Used for cell search and identification by the UE. Carries part of the cell ID (one of three orthogonal sequences)

Secondary synchronization signal
Used for cell search and identification by the UE. Carries the remainder of the cell ID (one of168 binary sequences)
Reference signal
Used for downlink channel estimation. Exact sequence derived from cell ID
(one of 3 x 168 = 504 pseudo random sequences)
Uplink physical signals
Purpose

Reference signals(demodulation
and sounding)
Used for synchronization to the UE and for UL channel estimation


LTE physical channels
DL channels
Full name
Purpose
PBCH
Physical broadcast channel
Carries cell-specific information
PMCH
Physical multicast channel
Carries the MCH transport channel
PDCCH
Physical downlink control channel
Scheduling, ACK/NACK
PDSCH
Physical downlink shared channel
Payload
PCFICH
Physical control format indicator channel

Defines number of PDCCH OFDMA symbols per subframe (1, 2, 3, or 4)
PHICH
Physical hybrid ARQ indicator channel

Carries HARQ ACK/NACK

UL channels
Full name
Purpose

PRACH
Physical random access channel
Random Access Procedure for Call Setup
PUCCH
Physical uplink control channel
Scheduling, ACK/NACK
PUSCH
Physical uplink shared channel
Payload

  
Physical layer procedures

-        Cell search
-        Power control
-        Uplink synchronisation and Uplink timing control
-        Random access related procedures
-        HARQ related procedures

2 comments:

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  2. A very good comparison for LTE Physical layer with HSPA.

    http://telecomfunda.com/lte-physical-layer-compared-to-hspa/

    ReplyDelete