4G/LTE - PHY Channel

  

 

 

 

PCFICH (Physical Control Format Indicator Channel)

 

The literal meaning of PCFICH is the Physical Channel that carries CFI (Control Format Indicator). As you see in Downlink Frame Structure page, it is described as follows :

  • It carries the number of symbols that can be used for control channels (PDCCH and PHICH).
  • Mapped to the first OFDM symbol in each of the downlink sub-frameThis contains the information on number of OFDM symbols for PDCCH and PHICH symbol duration received from the PBCHUE decode this channel to figure out how many OFDM symbols are assigned for PDCCH
  • It is 16 data subcarriers of the first OFDM symbol of the subframe.
  • PCFICH data is carried by 4 REGs and these four REGs are evenly distributed across the whole band regardless of the bandwidth.
  • The exact position of PCFICH is determined by cell ID and bandwidth.

 

< Overall Channel Processing >

 

The steps to process PCFICH (Converting CFI into physical symbols) is illustrated as follows. If you are interested seriously in details of physical layer channel processing, this can be one of the good place to start. It is much simpler than PDSCH or PBCH processing, but still has all the essense of channel processing.

If you want to have some hands-on this process and visualize the final result of this process, refer to Matlab : Toolbox : PCFICH.

 

 

< Information Carried by PCFICH >

 

With high level view, the information carried by PCFICH is simple. It is CFI number which can be 1 or 2 or 3. (For the detailed meaning and implication of CFI, refer to CFI page)

 

 

 

< Location of PCFICH >

 

Regardless of System Bandwidth, PCFICH is always carried by 4 REGs (16 REs) at the first symbol of each subframe. The exact location of these four REGs for PCFICH is determined by Physical Cell ID and System BW according to formula as shown below.