LTE PDCCH Calculator and CCE Index Calculation

This article explains the LTE PDCCH Calculator and its use in determining the CCE (Control Channel Element) Index based on the Aggregation Level or PDCCH formats. We’ll also cover the formula used in the calculation.

Understanding CCEs

CCE stands for Control Channel Element. Each CCE comprises 36 REs (Resource Elements), which translates to 72 bits when using QPSK modulation.

PDCCH Formats and Aggregation Levels

The PDCCH format corresponds to the following aggregation levels:

• PDCCH format 0: Aggregation level of 1
• PDCCH format 1: Aggregation level of 2
• PDCCH format 2: Aggregation level of 4
• PDCCH format 3: Aggregation level of 8

Examples:

• If the CCE Index is 0 and the aggregation level is 4, the PDCCH occupies CCE positions 0 to 3.
• If the CCE index is 4 and the aggregation level is 4, the PDCCH occupies CCE positions 4 to 7.
• If the CCE index is 0 and the aggregation level is 8, the PDCCH occupies CCE positions 0 to 7.

LTE PDCCH Calculator and Example

Let’s consider an example for CCE Index calculation:

Input:

• Aggregation level (L) = 1
• N_CCE = 100 (Number of CCEs)
• Subframe (k) = 1

Output:

• CCE Index = 49

The table below illustrates the CCE Index calculation for different subframes with intermediate outputs (yk and y(k-1)).

LTE CCE Index Calculation Formula

The following formula is used in the LTE PDCCH Calculator:

Where:

• L = Aggregation levels (1, 2, 4, or 8)
• N_CCE = Number of CCEs available for the PDCCH channel type
• m = Range from 0 to (Number of PDCCH candidates - 1)
• i = Range from 0 to (L - 1)
• Yk = A * (Yk-1) mod D
• k = Subframe number
• A = Constant value of 39827
• D = Constant value of 65537
• For k = 0, (Yk-1) = RNTI value of UE (User Equipment). Assuming RNTI = 100 in this case.