How we know about PDSCH location from PDCCH?

Question

N numbers of UEs can be scheduled at a particular TTI. So How does an UE get to know its own DCI ?

Answer 1

Hi,
Cosider an RB which consider 7 ofdm symbols and 12 sub carriers. Pcfich value either 1 or 2 or 3 which describes how many ofdm symbols carriers control info. Let's consider Pcfich value as 3, which means first 3 ofdm symbols in a RB carriers control info. This control info consists RE's of pdcch, Pcfich, phich and reference siganlas.. Apart from these control info remaining is for pdsch. In the control info pdcch carries the information about pdsch in form of dci's. Dci can give info about how many RBs for particular UE and which is the starting RB. By successful decoding of Dci, UE can came to know about its Pdsch allocation.. Hope it's clear.. Please let me know if you have any other queries regarding this question

Comments

Pcfich carries number of symbol s carried by pdcch right but u are telling pcfich carries remaining control channel info also?

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PCFICH value just tell in how many symbols PDCCh info consists.. let say pcfitch cfi value is 3.. it means in first 3 symbols of RB pdcch info consists. but in these 3 symbols along with PDCCH other REs for reference signal, PHICH and PCFICH also carries. To know only about PDCCH we should remove REs of above mentioned info from the total REs available in 3 symbols.

Answer 2

Every sub frame carries PDCCH information. The no. of symbols are being used for PDCCH informed by PCFICH.
Since UE has already synchronized with Cell, it knows about the location of RS in frequency and time domain. It also knows whether it is first sub radio frame or second sub radio frame of current radio frame. It removes the information from slot and get the PDSCH location in slots (first and second) of a particular sub radio frame.
As per my knowledge, eNodeB does not transmit location of PDSCH separately.

Answer 3

Hi,

In PDCCH we will receive DCI for the scheduling information about PDSCH. Say for e.g RAT 2 ENB will send starting RB and ending RB so based on this UE will come to know PDSCH location.

Answer 4

PDCCH is comprised of fixed DCI formats which contain specific details for PDSCH assignment (i.e. no. of slots, RBS, modulation etc.). Different DCI formats are used for different UE states, different MIMO states and whether it is UL or DL allocation? UE scans all possible PDCCH search spaces based on its state (SI-RNTI, P-RNTI, RA-RNTI, C-RNTI etc.) and decodes specific DCI format to get its assigned PDSCH.