Understanding 5G NR Numerologies

The 5G New Radio (NR) physical layer is designed to be highly flexible to support diverse use cases. One of the key enablers of this flexibility is the concept of scalable numerology.

What is Numerology?

In OFDM systems, numerology refers to the configuration of waveform parameters, specifically the Subcarrier Spacing (SCS) and the Cyclic Prefix (CP).

Unlike LTE, which supported a fixed SCS of 15 kHz, 5G NR supports multiple SCS values derived from the formula:

Delta f = 2^mu * 15 kHz

Where mu is the numerology index (0, 1, 2, 3, 4).

Why Scalable SCS?

1. Latency: Higher SCS means shorter symbol duration, leading to shorter slots and lower latency.
2. Phase Noise: Higher SCS is robust against phase noise, which is critical at higher frequencies (mmWave).
3. Doppler Shift: Wide SCS handles high Doppler shifts better (High-Speed Trains).

[!NOTE] Most commercial 5G networks in the C-Band (3.5 GHz) use 30 kHz SCS (mu=1).

Conclusion

Understanding numerology is the first step in mastering the 5G physical layer. It dictates the frame structure, resource grid, and ultimately the throughput capabilities of the cell.