This tutorial explains how LTE downlink maximum throughput is determined. This is a simple and straightforward formula for data rate calculation.
The maximum data rate depends on channel bandwidth. As LTE uses different channel bandwidths both for FDD and TDD.
Let’s take the example for LTE using FDD, where channel bandwidth can be 5 MHz, 10 MHz and 20 MHz. In LTE release 8 there is no carrier aggregation, so let’s just consider simple cases.
Here we are calculating maximum data rate at the physical layer. The data rate always depends on the channel bandwidth. For example, in case of 5 MHz channel bandwidth, 300 subcarriers are used.
For a perfect idle condition 64 QAM can be used. That means each symbol is now allowed to carry 6 bits.
So the total bits carried by 300 subcarriers for the duration of a symbol is 300 X 6 = 1800 bits.
Again 1 symbol is of 71.4 microseconds for LTE. So the data rate is 1800 / 71.4 = 25.2 Mbps.
So the formula for calculating maximum data rate at physical layer is:
(Number of subcarriers X 6) / 71.4 microseconds
For 10 MHz using the same formula the maximum data rate in downlink is 50.4 Mbps and for 20 MHz it is 100.8 Mbps.