We have discussed PCFICH resource mapping, PHICH resource mapping, and PDCCH construction. Now we are ready to look at PDCCH dimensioning. Since the PDCCH is constructed from Control Channel Elements (CCEs) with an aggregation level of 1, 2, 4, or 8, we'll calculate how many CCEs are available.
Let's use the table "PDCCH Dimensioning (10 MHz)" channel bandwidth as an example. We assume 1 or 2 or 3 OFDM symbols are allocated for PDCCH.
An exercise for you: calculate the number of available CCEs if 2 or 3 OFDM symbols are allocated for the PDCCH.
Similarly, we can also calculate PDCCH dimensioning for 5 MHz and 20 MHz channels.
What does the number of available CCEs indicate? It is a good indication of PDCCH capacity, such as how many UEs can be scheduled per subframe. Note that the PDCCH carries resource allocations for both user traffic and control signaling messages. The control signaling overhead includes SIBs, paging, PRACH response, and uplink Transmit Power Control (TPC) commands. The frequency of the control signaling transmission depends on the system configuration.
Knowing the PDCCH capacity, dynamic PDCCH allocation can be used to improve throughput. If the number of active users is low, fewer OFDM symbols are used; if there are more active users in the system, more OFDM symbols will be allocated for the PDCCH.
PDCCH capacity does not generally impact the throughput of data traffic that can tolerate more delay. For delay-sensitive traffic such as Voice over IP (VoIP), PDCCH capacity and utilization need to be carefully monitored for any potential negative impact.
What is the significance of the parameter Maximum number of OFDM symbols for PDCCH, As we see that for 2CCE(aggregation level -2) are sufficient for DCI format 2, so when do we need this parameter to incresae PDCCH capacity.
If it is for expansion , then how CCE of PDCCH are allocated to UE, IS it 2CCE(AL2) per user ?
Dear Hongyan ;
many thanks for this details about PDCCH Dimensioning.
can you please explain briefly the PDSCH Dimensioning .