What is LTE Maximum Downlink Throughput?

4G LTE
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Hello Experts,

Speaking about LTE theoretical limits, what is LTE Maximum Downlink Throughput?

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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.

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We often hear that the peak data rate of LTE is about 300 Mbps.

Let’s estimate it in a simple way.
Assume 20 MHz channel bandwidth, normal CP, 4x4 MIMO.

  • First, calculate the number of resource elements (RE) in a subframe with 20 MHz channel bandwidth: 12 subcarriers x 7 OFDMA symbols x 100 resource blocks x 2 slots= 16800 REs per subframe. Each RE can carry a modulation symbol.

  • Second, assume 64 QAM modulation and no coding, one modulation symbol will carry 6 bits. The total bits in a subframe (1ms) over 20 MHz channel is 16800 modulation symbols x 6 bits / modulation symbol = 100800 bits. So the data rate is 100800 bits / 1 ms = 100.8 Mbps.

  • Third, with 4x4 MIMO, the peak data rate goes up to 100.8 Mbps x 4 = 403 Mbps.

  • Fourth, estimate about 25% overhead such as PDCCH, reference signal, sync signals, PBCH, and some coding. We get 403 Mbps x 0.75 = 302 Mbps.

Is there a way to calculate it more accurately?

If this is what you look for, you need to check the 3GPP specs 36.213, table 7.1.7.1-1 and table 7.1.7.2.1-1.

Table 7.1.7.1-1 shows the mapping between MCS (Modulation and Coding Scheme) index and TBS (Transport Block Size) index.
Let’s pick the highest MCS index 28 (64 QAM with the least coding), which is mapping to TBS index of 26.

Table 7.1.7.2.1-1 shows the transport block size. It indicates the number of bits that can be transmitted in a subframe/TTI (Transmit Time Interval).
For example, with 100 RBs and TBS index of 26, the TBS is 75376. Assume 4x4 MIMO, the peak data rate will be 75376 x 4 = 301.5 Mbps.

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Hello @Rafael_Caixeta,

You can use the calculator available at our resources page, and see estimated calculation based on MIMO, MOdulation, Bandwidth, etc…

Telecom Calculators (4G Theoretical Throughput Calculator)

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You are right ,
In LTE for 20 MHz, there are 100 Resource Blocks and each Resource block have 12x7x2=168 Symbols per ms in case of Normal CP.
So there are 16800 Symbols per ms or 16800000 Symbols per second or16.8 Msps. If modulation used is 64 QAM (6 bits per symbol) then throughput will be 16.8x6=100.8Mbps for a single chain.
For a LTE system with 4x4 MIMO (4T4R) the throughput will be four times of single chain throughput. i.e. 403.2 Mbps.

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What is maximum speed of LTE TDD where we have 4x4 MIMO, 256 QAM for DL and BW is 20MHz?