5G New Radio (NR) introduces a significant departure from LTE by offering a flexible Orthogonal Frequency Division Multiplexing (OFDM) numerology, which includes variable subcarrier spacing. Here’s how 5G NR’s subcarrier spacing differs from LTE:
- Flexible Subcarrier Spacing: 5G NR supports a range of subcarrier spacings, which can vary from 15 kHz to 240 kHz. This flexibility allows 5G NR to be highly adaptable to different use cases, frequency bands, and service requirements.
- Proportional Cyclic Prefix: As the subcarrier spacing changes, the duration of the cyclic prefix is adjusted proportionally. The cyclic prefix remains an essential component of OFDM to maintain orthogonality between subcarriers. In other words, the guard interval adapts to the subcarrier spacing to ensure efficient communication.
Numerology – Subcarrier Spacing
5G subcarrier spacing (SCS) is the distance between two adjacent subcarriers in an OFDM (Orthogonal Frequency Division Multiplexing) signal. It is a key parameter that affects the bandwidth and performance of a 5G network.
5G NR supports a variety of SCS values, including 15 kHz, 30 kHz, 60 kHz, 120 kHz, and 240 kHz. These SCS values are mapped to numerologies 0, 1, 2, 3, and 4, respectively.
SCS = 15 * 2^μ
μ is the numerology
Consider the following example:
Subcarrier spacing: 30 kHz
Using the formulae above, we can calculate the following parameters:
OFDM symbol duration = 10^3 / (14 * 2^1) = 35 μs
Number of OFDM symbols per slot = 14 * 2^1 = 28
Cyclic prefix duration = 4.7 μs
Subframe duration = 1 ms
Radio frame duration = 10 ms
Below diagram will be showing subcarrier mapping based on numerology
A higher numerology indicates a wider SCS. This means that there are fewer subcarriers, but each subcarrier is wider. Wider subcarriers are more resistant to interference, but they also require more bandwidth.
The choice of numerology depends on a number of factors, including the desired bandwidth, the available spectrum, and the channel conditions. For example, a high numerology with a wide SCS may be used in a macrocell deployment to provide high throughput to users over a large area. A low numerology with a narrow SCS may be used in a small cell deployment to provide high reliability to users in dense urban areas.
Supported Channel mapping with numerology
- It’s Not like that every numerology can be used for every physical channel.
- Numerologies has been specified as per certain type of physical channel.
This means that not every numerology, which is a set of parameters that define the physical layer structure of a 5G NR system, can be used for every physical channel. There are specific numerologies that are specified for certain types of physical channels.