LTE Code Rate Calculator and Calculation

This page explains the LTE Code Rate Calculator and how it works. The calculation of the LTE code rate depends on several factors: the Modulation and Coding Scheme (MCS), the number of Physical Resource Blocks (PRBs), and the number of OFDM symbols per slot.

The calculator outputs the code rate, taking into account the percentage of Resource Elements (REs) used in control channel operation. PRBs are the Physical Resource Blocks allocated to the User Equipment (UE) by the evolved NodeB (eNB). MCS refers to the Modulation and Coding Scheme used.

LTE Code Rate Calculator Example

• Input:
  • MCS = 20
  • Number of PRBs = 2
  • OFDM symbols per slot = 7
  • REs for control channel (%) = 10
• Outputs:
  • Code rate = 0.44
  • Number of bits/subcarrier = 6 bits
  • TBS size = 776 bits

LTE Code Rate Calculation Method

The following equations are used in the LTE Code Rate Calculator:

• Equation-1: LTE Code Rate = (TBS + CRC)/(N_REs*Qm)
• Equation-2: N_REs = N_PRBs*12*N_symbols*2* (1-((percent_REs_CC/100)))

Where:

• N_symbols = Number of OFDM symbols in a slot (7 for normal cyclic prefix and 6 for extended cyclic prefix).

Steps for LTE Code Rate Calculation:

• Step-1: Determine Qm and TBS Index (I TBS ) from MCS based on Table 7.1.7.1-1 (shown below).
  • Qm = Bits per RE as per modulation scheme (2 for QPSK, 4 for 16QAM, and 6 for 64QAM).
• Step-2: Using the I TBS obtained in step-1 and the N_PRBs entered by the user, find the TBS (Transport Block Size) from table 7.1.7.2.1-1 in the 3GPP TS 36.213 V9.2.0 standard. A portion of this table is shown below for explanatory purposes.
• Step-3: Calculate the LTE code rate by plugging the TBS (from step-2), Qm (from step-1), and CRC (Cyclic Redundancy Check, which is 24 bits) into Equation-1. Calculate N_REs using Equation-2.

Tables

Table-1: LTE MCS Table

Table-2: LTE TBS Table

The LTE code rate calculator utilizes all 11 tables of Transport Block Size mentioned in the 3GPP TS 36.213 document. These tables contain the TBS size for I TBS ranging from 0 to 26 and N PRB ranging from 1 to 110. This LTE code rate calculation is very useful for LTE system designers and LTE test teams.