5G NR Data Rate Calculation — Step by Step

A common question that most telecom experts are interested in is: what is the maximum data rate supported by 5G? These peak numbers are unrealistic in real-world deployments, but understanding how to calculate them gives deep insight into the 5G NR air interface.

In this post, we calculate and explain the maximum data rate from first principles — starting with a single PRB and working up to 12-layer MU-MIMO.

Step 1: Start With a Single PRB

Irrespective of bandwidth and subcarrier spacing, the number of subcarriers in a Physical Resource Block (PRB) is always constant: 12 subcarriers.

1 PRB STRUCTURE (normal slot)

12 subcarriers × 14 OFDM symbols = 168 Resource Elements (REs)

Breakdown: PDCCH (12 RE) + DMRS (6 RE) + PDSCH (150 RE)

Step 2: Calculate PDSCH REs (Single Layer)

A single PRB with 12 subcarriers and 14 OFDM symbols contains mainly three types of signals in the downlink: PDCCH, PDSCH, and PDSCH-DMRS (ignoring CSI-RS, PTRS for simplicity).

Element	REs	Purpose
Total REs in PRB	168	12 × 14
PDCCH REs	−12	Control channel overhead
DMRS REs	−6	Single-symbol DMRS, type 1
PDSCH REs	150	Data-carrying REs

Signaling overhead = 18/168 = 10.71%

Step 3: Scale to Full Bandwidth

For 100 MHz bandwidth with 30 kHz SCS, the total number of PRBs is 273, and each slot is 500 µs.

Total PDSCH REs = 273 PRBs × 150 REs/PRB = 40,950 REs per slot

With the highest MCS (code rate = 948/1024, modulation = 256 QAM → 8 bits/RE):

Bits per slot = 40,950 × 8 × (948/1024) ≈ 303,285 bits

Converting to throughput (slot = 500 µs):

Single-layer DL throughput ≈ 606.6 Mbps

Step 4: Scaling to 12-Layer MU-MIMO

3GPP defines up to 12 layers in the downlink for Multi-User MIMO. With more layers, we need a different DMRS configuration to support layer separation.

For 12 layers, we use double symbol DMRS with DMRS configuration Type 2 (all 3 CDM groups). This increases the DMRS overhead:

Config	DMRS REs	PDSCH REs	Overhead
Single layer (single symbol DMRS, type 1)	6	150	10.71%
12 layers (double symbol DMRS, type 2, all CDM groups)	36	132	21.43%

Maximum data rate with 12 layers, 100 MHz, 30 kHz SCS, 256 QAM, code rate 948/1024:

Bits = 12 × 273 × 132 × 8 × (948/1024) ≈ 3,202,699 bits per slot

Peak DL throughput (12 layers, 100 MHz, 30kHz SCS) ≈ 6.4 Gbps

The 3GPP Standard Formula

The official formula from 3GPP TS 38.306 calculates the approximate maximum data rate in bits per second. For carrier aggregation:

Data Rate = Σ_c=1..Nc [ v_Layers^c · Q_m^c · f^c · R_max^c · (N_PRB^BW(c),µ · 12) / T_s^µ · (1 − OH^c) ]

Parameter	Description
`N_c`	Total number of component carriers (carrier aggregation)
`v`	Number of MIMO layers
`Q_m`	Modulation order (2=QPSK, 4=16QAM, 6=64QAM, 8=256QAM)
`f^c`	Scaling factor: 1, 0.8, 0.75, or 0.4 (signaled by RRC)
`R_max`	Maximum code rate = 948/1024
`N_PRB`	Max number of resource blocks for the bandwidth
`T_s^µ`	Average OFDM symbol duration (depends on numerology µ)
`OH`	Signaling overhead fraction

Standard Overhead Values (3GPP)

Frequency Range	Direction	Overhead
FR1 (sub-6 GHz)	Downlink	0.14 (14%)
FR2 (mmWave)	Downlink	0.18 (18%)
FR1 (sub-6 GHz)	Uplink	0.08 (8%)
FR2 (mmWave)	Uplink	0.10 (10%)

Key Takeaways

Five factors directly determine the 5G NR data rate:

Bandwidth: More PRBs = linearly more capacity
Modulation: 256QAM carries 4× more bits per RE than QPSK
Layers: 12 layers = 12× the capacity, but DMRS overhead increases too
Code rate: Higher code rate = more information bits per transmitted bit
Overhead: DMRS, PDCCH, and control signals consume a fraction of capacity

The 6.4 Gbps peak for a single 100 MHz carrier in FR1 represents the theoretical ceiling. Real-world deployments achieve far lower rates due to channel conditions, interference, and practical layer limitations.

📡