Calculate PDCCH capacity in CCEs and estimate the maximum users schedulable per TTI.
Max users schedulable per TTI (DL)
Total REs in control region
Available REs (after CRS, PCFICH, PHICH)
Available REGs
Total CCEs available
Aggregation level
Max users per TTI
Actual capacity is less due to search space constraints and UE-specific PDCCH overhead. This calculator gives a theoretical upper bound. The common search space further limits simultaneous scheduling.
Frequently Asked Questions
What is a CCE in LTE?
A CCE (Control Channel Element) is the basic resource unit of the LTE PDCCH. One CCE consists of 9 REGs (Resource Element Groups), where each REG contains 4 resource elements. The PDCCH carries DCI messages that tell UEs which time-frequency resources to use for PDSCH and PUSCH. The total CCE count per subframe depends on the system bandwidth and the number of OFDM symbols allocated to the control region (CFI).
What is CFI in LTE PDCCH?
CFI (Control Format Indicator) tells the UE how many OFDM symbols (1, 2, or 3) at the start of each subframe are used for the PDCCH region. A higher CFI means more control capacity (more CCEs) but fewer symbols available for PDSCH data. CFI=1 is preferred for wide bandwidths (≥10 MHz); CFI=3 is used for narrow bandwidths or high control overhead scenarios. The CFI is transmitted via the PCFICH channel.
How does aggregation level affect PDCCH capacity?
The PDCCH aggregation level determines how many consecutive CCEs carry a single DCI message. Aggregation level 1 is used near the cell center (good SNR), enabling many simultaneous users. Aggregation level 8 is used at the cell edge (poor SNR), using more redundancy to ensure reliable reception but drastically reducing the number of users schedulable per TTI. A cell with 20 available CCEs can schedule 20 users at AL1 but only 2 users at AL8.