LTE- UPLINK Physical layer Singnalling.

Up link L1/L2 control signalling is divided into two classes in the LTE system

1. Control signalling in absence of up-link data , which is done by PUCCH ( Physical up-link control channel) i.e when the UE is in IDLE Mode and has no dedicated resources allocated to it, only then the control signalling is carried on PUCCH.

2. Control signalling in presence of up-link data, which takes place on PUSCH ( Physical up-link shared channel ) i.e. when the UE is in CONNECTED mode and has dedicated resources allocated to it.

As uplink transmission is done using SC-FDMA i,e single carrier transmission, there are some limitations due to which simultaneous transmission of PUCCH and PUSCH is not allowed. Due to this separate control resources are defined for with and without up-link data.

PUCCH is a shared channel and is optimized for UL  control signalling for large number of UE's Simultaneously. PUCCH is a shared frequency/time resource which are reserved exclusively for UE transmitting L1/L2 control signalling data. PUCCH is optimized for large number of UE's for a small number of control bits per UE.

PUSCH carries L1/L2 up-link control signalling data when the UE is in connected mode i.e. it is scheduled for up-link data transfer. PUSCH is capable of transmitting control signalling with large rage of signalling sizes.

There are two types of up-link L1/L2 control signalling information

1. Data associated signalling (eg. transport block, HARQ info ) which is usually associated with up-link data transmission
2. Data non-associated signalling ( ACK/NAK due to down-link signalling , Down-link Chanel quality index (CQI) and scheduling requests of up-link data transmission.     

Mohiuddin Syed

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