So far I’ve always made a quick and approximate calculation when somebody asked me what the theoretical peak data rate of 5G NR would be for a given bandwidth. But there is a more scientific way to do this as 3GPP has put a formula together to include all relevant factors in the calculation. Using this formula it is then possible to not only calculate the theoretical peak throughput but also what can be achieved in realistic transmission conditions. As the number of parameters that go into the calculation is quite lengthy a number of people have made online calculators available. Here’s a good example.
Let’s assume that a network operator does have 100 MHz of spectrum in the 3.5 GHz range for 5G NR. In this case the maximum throughput with the maximum number of 273 RBs assigned to the device, minus the scheduling and management overhead is 2.337 Gbit/s with 4×4 MIMO and 256 QAM modulation. But that’s for an FDD system, band n78 is TDD and the channel is thus shared between uplink and downlink. So let’s assume there is a 3:1 DDDSU pattern with 3 downlink slots (D), 1 uplink slot (U) and a special slot with 80% downlink and the rest for direction switching. That would be a ratio of 3.8 : 5 and the resulting data rate would thus be 1,776 GBit/s. In addition to that let’s say the network bundles 3 LTE carriers with 20 MHz each to the 5G NR 100 MHz carrier. In other words, that’s an additional 60 MHz of spectrum pressed into action. With 4×4 MIMO and 256-QAM one can get a theoretical maximum of around 375 Mbit/s out of a 20 MHz channel. That would be 1,125 Gbit/s in addition for a theoretical total of 2.901 Gbit/s.
But let’s get back down to earth. In practice one might get that much of spectrum assigned by the network for data transmission but even close to the base station it is really hard to get ideal conditions. In most cases 2×2 MIMO is much more realistic and one gets quickly bumped down from 256QAM to 64QAM as well. Also, let’s factor in that most network operators do not have three 20 MHz LTE channels, so let’s go for 50 MHz instead. With these figures, the 5G NR speed on the 100 MHz channel is 876 Mbit/s and LTE throughput will be 375 Mbit/s, 1.251 Mbit/s in total.
Note that there are two parameters that are not part of the formula as it focuses on throughput and not on capacity: One thing to also account for in practice is that one is usually not alone in a cell, so capacity has to be shared with others that transfer data simultaneously. On the other hand, the promise of Multi-User MIMO (MU-MIMO) is to serve several users that are close to the base station simultaneously in the same resource blocks. So there are some gains to be expected here when it comes to overall cell capacity.