A common question, most telecom experts are interested in is, the maximum data rate supported. These numbers are unrealistic in real life. Data rate calculations are different in 4G and 5G.

In this post, we will calculate and understand the maximum data rate.

Let’s start with downlink with a single PRB. Irrespective of bandwidth & subcarrier spacings, the number of subcarriers in a PRB are constant

A PRB as shown above with 12 subcarriers and 14 OFDM symbols mainly has 3 different types of signals/channels in DL: PDCCH, PDSCH, and PDSCH-DMRS (for now we will skip CSI-RS, PTRS etc.).

Total number of Resource Elements (REs) in a PRB = 12 * 14 = 168 REs

Total number of PDSCH REs in a PRB for the above case = 168 – PDSCH REs – DMRS REs = 168 – 12 – 6 = 150 REs

These remaining REs are called signaling overhead (OH). In the case, the overhead is = 18 REs = 18/168 = 10.71%

Resources occupied by PDSCH = 150 REs = 150/168 = 89.29%

Let’s calculate the total number of REs in the full band with the above overhead. Considering 100 MHz bandwidth and 30kHz subcarrier spacing, the total number of PRBs are 273 in 500 microseconds. Therefore, total PDSCH REs are 273 * 150 = 40950 REs.

By considering the highest MCS (code rate = 948/1024, modulation = 256 QAM), the total number of bits that can be mapped to the above (40950) REs are 40950 * 8 * 948/1024 ~ 303285 in 500 microseconds.

Therefore, for a single layer, 100 MHz bandwidth with 30 kHz subcarrier spacing and with 10.71% signaling overhead, we can transmit 303285 bits in 500 microseconds which are 606571 K bits per second = 606.571 Mbps

3gpp defines 12 layers in the downlink for the Multi-User MIMO case. For such a transmission DMRS configurations are different. Therefore, considering the double symbol DMRS and DMRS configuration type 2 for all the 12 layers (all 3 CDM groups), the resource allocation looks like follows:

Therefore, the overhead is 36/168 = 21.43%

By considering 100 MHz bandwidth with 30 kHz subcarrier spacing and the highest MCS (code rate = 948/1024, modulation = 256 QAM), the total number of bits that can be mapped to the REs are 12 (layers) * 273 (PRBs) * 132 (REs in a PRB) * 8 (Qm) * 948/1024 (code rate) ~ 3202699 in 500 microseconds.

Therefore, for 12 layers, 100 MHz bandwidth with 30 kHz subcarrier spacing, and with 21.43% signaling overhead, we can transmit 3202699 bits in 500 microseconds which are 6405399 K bits per second ~ 6.4054 Gbps

**6.4054 is the highest data rate in downlink for a single carrier with 21.43% overhead.**

For different signaling overheads, the maximum data rate can be different. We can assume the following values of overhead (OH):

FR1/FR2 | DL/UL | Overhead |

FR1 | DL | 0.14 |

FR2 | DL | 0.18 |

FR1 | UL | 0.08 |

FR2 | UL | 0.10 |

The following formula calculates the approximate data rate in bits per sec (bps):

The above formula uses the following parameters:

- Nc: Total number of component carriers for carrier aggregation
- v: Number of layers
- Qm: Modulation order
- fc: Scaling factor. This is signaled by higher layers. Allowed values are 1, 0.8, 0.75, or 0.4.
- Rmax: Maximum possible code rate
- N_PRB: Maximum number of resource blocks
- Ts: Average symbol duration
- OH: Overhead due to signaling information

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