PHY - PDCCH

PDCCH - Physical Downlink Control Channel

PDCCH is the most important downlink channel which carries the control information to the UE's. It tells the UE's 2 most important things.

1. Where the Downlink Data is in the current subframe for the UE.
2. Which UE need to transmit the UL data now.

PDCCH is transmitted in PDCCH Quadruplets of 4 RE's each. So 9 PDCCH Quadruplets or 9 REG's comprises 1 CCE

So the number of PDCCH Quadruplets transmitted will differ based on 2 factors.

1. Channel Bandwidth
2. Number of UE's & amount of control information to be sent for each UE.

In general Higher the BW, higher the PDCCH Quadruplets usage. We will see more about the CCE's & DCI carried by the PDCCH in the upcoming blogs.

Important notes on PDCCH:

1. PDCCH will always be carried on 1st the symbol on every subframe.
2. Depending on the PDCCH format, the number of symbols used for PDCCH will change in every subframe.
3. PDCCH format 1, 2, 3 used for all the Channel Bandwidth's. In addition format 4 which uses the 4th OFDM symbol in a subframe is used only in the 1.4Mhz channel BW.
4. PDCCH always uses QPSK modulation.