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

Inputs Clear Input

Aggregation Level (Enter: 1/2/4/8):

Number of CCEs (N_CCE):

Subframe Number, k (Enter: Range 0 to 9):

Outputs Calculate

LTE CCE Index for PDCCH channel (Output#1):

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)).

K (subframe number)	Y(k-1)	Y(k)	N_CCE	CCE Index
0	100	50480	100	81
1	50480	53948	100	49
2	53948	21988	100	89
3	21988	10682	100	83
4	10682	31347	100	48
5	31347	42656	100	57
6	42656	10398	100	99
7	10398	58380	100	81
8	58380	44111	100	12
9	44111	23975	100	76

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.

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Continue Learning 4G LTE

• 4G LTE Basics Tutorial
• 4G LTE Architecture: Network Elements and Interfaces
• LTE Channel Types: Logical, Transport and Physical Channels
• LTE Protocol Stack: User Plane vs. Control Plane
• 4G LTE Physical Layer & its modules
• LTE Frequency Bands: FDD, TDD and E-UTRA Bands
• LTE Carrier Aggregation & its benefits
• 4G LTE Network Security
• LTE Cell Search Procedure
• LTE UE Uplink Network Entry : Random Access Procedure
• LTE Paging Procedure Mechanism and Call Flow