As the telecommunications industry transitions from LTE (4G) to 5G NR (New Radio), several new concepts and enhancements are introduced to accommodate the increasing demands for faster, more reliable, and flexible wireless communication. One of these key concepts is 5G Numerology. As a telecommunications engineer, this article will delve into what numerology is in the context of 5G NR, its components, and the advantages it brings over LTE.

What is 5G Numerology?

5G Numerology refers to a set of parameters that define how the 5G radio waveforms are structured. These parameters include subcarrier spacing (SCS), symbol duration, and cyclic prefix (CP) length. Unlike LTE, which uses a fixed 15 kHz subcarrier spacing, 5G NR introduces multiple subcarrier spacings to support a wide variety of use cases and deployment scenarios.

Components of 5G Numerology

Subcarrier Spacing (SCS):

SCS is the spacing between adjacent subcarriers in the frequency domain. In 5G NR, SCS can be expressed as:

SCS = 15 kHz × 2^μ
where (mu) is a numerology index that can take integer values from 0 to 4.

Symbol Duration:

The duration of one OFDM symbol is inversely proportional to the subcarrier spacing. As SCS increases, the symbol duration decreases, which helps in reducing latency.

Cyclic Prefix (CP):

CP is a guard interval inserted between OFDM symbols to mitigate inter-symbol interference (ISI). 5G NR supports both normal and extended CP, with extended CP primarily used in scenarios requiring higher robustness, such as high mobility environments.

Advantages of 5G NR over LTE.

Enhanced Use Cases:

Enhanced Mobile Broadband (eMBB): Provides higher data rates and better coverage for applications like high-definition video streaming and VR/AR.
Ultra-Reliable and Low Latency Communications (URLLC): Supports mission-critical applications requiring extremely low latency and high reliability, such as autonomous driving and industrial automation.
Massive Machine-Type Communications (mMTC): Facilitates the connection of a large number of IoT devices with efficient signaling and low power consumption.

Flexible Spectrum Utilization:

5G NR can utilize a wider range of spectrum, including both sub-6 GHz (FR1) and mmWave frequencies (FR2).
FR1 covers frequencies below 6 GHz, while FR2 spans from 24 GHz to 52 GHz, allowing for higher bandwidth and data rates.

Support for High-Speed Mobility:

5G NR is designed to maintain reliable connections for UEs moving at speeds up to 500 km/h, which is essential for high-speed trains and other fast-moving vehicles.

5G Numerologies Defined in 3GPP TS 38.211.

The table below summarizes the numerologies supported in 5G NR, as defined in 3GPP TS 38.211:

μ	SCS	CP	Corresponding Frequency Range
0	15	Normal	FR1
1	30	Normal	FR1
2	60	Normal and Extended	FR1 and FR2
3	120	Normal	FR2
4	240	Normal	FR2

As shown, 5G NR supports five SCS values ranging from 15 kHz to 240 kHz. Both low and high-frequency bands support three SCSs each, with 60 kHz SCS supporting both normal and extended CPs across FR1 and FR2.

Practical Implications of 5G Numerology.

Doppler Shift Management:

For UEs moving at high speeds, the Doppler shift can significantly affect signal quality.
A larger SCS helps in minimizing the impact of Doppler shift, making it suitable for high-mobility scenarios.

Latency and Throughput Trade-offs:

Different SCSs allow for balancing between latency and throughput.
Lower SCSs (15 kHz, 30 kHz) are ideal for eMBB and mMTC due to their longer symbol duration, which provides better coverage and penetration.
Higher SCSs (120 kHz, 240 kHz) are better for URLLC due to their shorter symbol duration, which reduces latency.

Spectrum Efficiency:

The ability to use a wider range of subcarrier spacings allows for more efficient utilization of available spectrum.
This flexibility ensures that 5G networks can meet diverse service requirements, from dense urban areas to rural deployments.

Conclusion

5G Numerology is a foundational concept in 5G NR that introduces flexible subcarrier spacings and symbol durations to meet the varied demands of modern wireless communication. By understanding and leveraging 5G numerology, network operators can optimize their networks for enhanced performance, better coverage, and support for a wide range of use cases. This adaptability is one of the key factors that make 5G a revolutionary step forward from LTE.

References

3GPP TS 38.300, NR and NG-RAN Overall Description; Stage 2 (Release 16)
3GPP TS 38.101-1, User Equipment (UE) radio transmission and reception; Part 1: Range 1 Standalone (Release 16)
3GPP TS 38.101-2, User Equipment (UE) radio transmission and reception; Part 1: Range 2 Standalone (Release 16).
3GPP TS 38.104, Base Station (BS) radio transmission and reception (Release 16).
3GPP TS 36.211, Physical channels and modulation (Release 14).
3GPP TS 38.213, Physical layer procedures for control (Release 16).
3GPP TS 38.211, Physical channels and modulation (Release 16).
3GPP TR 38.912 (Release 15).
3GPP TR 38.802, Physical Layer Aspects (Release 14).

Following questions are asked during interview of 5G NR RAN, RF and Microwave on topic of Time Domain Resources.