In the rapidly evolving landscape of wireless technology, the concept of numerology has emerged as a foundational element for the design and deployment of 5G networks. While the term "numerology" is traditionally associated with the mystical significance of numbers, in the context of 5G New Radio (NR) standards, it refers to a systematic framework of parameters that define the physical layer waveform. This technical numerology is essential for supporting the diverse requirements of 5G applications, ranging from enhanced mobile broadband to ultra-reliable low-latency communications. The provided source material focuses exclusively on this telecommunications application of numerology, detailing the specific parameters that enable the flexibility and efficiency of 5G systems.
The core of 5G numerology lies in its ability to configure subcarrier spacing, symbol duration, and slot structure to match various deployment scenarios and frequency bands. As defined by the 3GPP NR release 15 standards, 5G utilizes a flexible frame structure where a 10 ms frame is divided into 10 subframes of 1 ms each. These subframes are further composed of slots, which contain multiple Orthogonal Frequency-Division Multiplexing (OFDM) symbols. The number of slots per subframe and the duration of these slots are determined by the numerology index, often denoted as μ. This index allows the system to adapt to different needs, such as minimizing latency for critical communications or maximizing spectral efficiency for wide-area coverage. The choice of subcarrier spacing, a key parameter in this numerology, presents a trade-off: smaller spacings enable higher data rates and efficient spectrum use, while larger spacings provide robustness against delay spread and Doppler effects, which are particularly important at higher frequencies.
A critical component of the 5G numerology table is the relationship between subcarrier spacing and symbol duration. The symbol duration (Ts) is inversely proportional to the subcarrier spacing (Δf), expressed mathematically as Ts = 1/Δf. For instance, a subcarrier spacing of 15 kHz results in a symbol duration of approximately 66.7 microseconds (μs). As the subcarrier spacing increases—for example, to 30 kHz, 60 kHz, 120 kHz, or even 240 kHz—the symbol duration decreases accordingly, down to 4.17 μs for 240 kHz spacing. This inverse relationship is fundamental to the system's design, influencing not only the data transmission rate but also the handling of multipath effects and the overall timing synchronization within the network. The ability to scale these parameters provides the versatility needed to support both low-frequency bands (FR1, below 6 GHz) and high-frequency millimeter-wave bands (FR2, above 24 GHz).
The structure of slots within the 5G frame is another vital aspect governed by the numerology. A slot is defined as a collection of OFDM symbols, with a standard configuration typically accommodating 14 symbols for normal Cyclic Prefix (CP) or 12 symbols for extended CP. The number of slots per subframe scales directly with the numerology index μ. For example, with μ = 0 (corresponding to 15 kHz spacing), there is 1 slot per subframe. As μ increases to 1, 2, 3, and 4, the slots per subframe increase to 2, 4, 8, and 16, respectively. Consequently, the number of slots per 10 ms frame also increases, from 10 slots for μ = 0 to 160 slots for μ = 4. This granular control over slot allocation allows the network to prioritize different types of traffic; a higher number of slots can facilitate rapid transmission for latency-sensitive applications, while fewer, longer slots can be used for efficiency in less demanding scenarios.
Furthermore, the numerology framework includes parameters such as the Cyclic Prefix duration, which mitigates inter-symbol interference, and the maximum nominal system bandwidth supported for each subcarrier spacing. The provided data illustrates that while FFT size remains constant at 4096 points for the considered configurations, the maximum bandwidth scales with subcarrier spacing, reaching up to 400 MHz for spacings of 120 kHz and 240 kHz. The number of Resource Blocks (RBs) is also dependent on the subcarrier spacing and the overall bandwidth. This detailed table of parameters—encompassing subcarrier spacing, symbol duration, CP duration, maximum bandwidth, FFT size, symbols per slot, and slots per frame/subframe—constitutes the essential technical "numerology" that enables 5G to deliver on its promise of high speed, low latency, and massive connectivity. This systematic approach ensures that the physical layer can be optimized for a wide array of use cases, from enhanced mobile broadband (eMBB) and massive machine-type communication (mMTC) to ultra-reliable low-latency communication (URLLC).
Key Parameters of 5G NR Numerology
The 5G NR numerology is characterized by a set of interrelated parameters that define the transmission timing and resource allocation. The primary parameters detailed in the source material include subcarrier spacing, symbol duration, Cyclic Prefix duration, and slot structure. The flexibility of these parameters is what distinguishes 5G from previous generations of wireless technology.
- Subcarrier Spacing (Δf): This is the fundamental parameter in the 5G numerology table. The standard defines several possible values: 15 kHz, 30 kHz, 60 kHz, 120 kHz, and 240 kHz. The selection of subcarrier spacing is a strategic decision based on the operational frequency band and the specific application. For low-frequency operations (FR1), smaller spacings like 15 kHz and 30 kHz are common, allowing for efficient use of the spectrum and good coverage. For high-frequency mmWave bands (FR2), larger spacings such as 120 kHz and 240 kHz are preferred to combat the increased phase noise and Doppler spread inherent at these frequencies. The choice directly impacts the trade-off between data rate and robustness.
- Symbol Duration (T_s): As established, the symbol duration is the reciprocal of the subcarrier spacing. This parameter dictates the time required to transmit a single OFDM symbol. A shorter symbol duration allows for more symbols to be transmitted in a given time interval, potentially increasing the data rate. However, it also makes the system more susceptible to delay spread, as the symbol duration must be significantly longer than the channel's delay spread to avoid inter-symbol interference. The Cyclic Prefix (CP) is added to each symbol to further mitigate this effect.
- Cyclic Prefix (CP) Duration: The CP is a guard interval added at the beginning of each OFDM symbol. Its duration is also dependent on the subcarrier spacing. For normal CP, the duration is relatively small (e.g., 4.7 μs for 15 kHz spacing) and scales down as spacing increases. For extended CP, which is an option primarily for 60 kHz spacing, the duration is longer (4.13 μs), making it suitable for scenarios with very large delay spreads, such as large cell deployments or certain multipath environments.
- Slot Structure and Duration: A slot is a time unit consisting of a fixed number of OFDM symbols (typically 14 for normal CP). The slot duration is therefore a function of the symbol duration and the number of symbols per slot. As the subcarrier spacing increases, the symbol duration decreases, and consequently, the slot duration decreases. This allows for finer scheduling granularity. For example, a slot at 15 kHz spacing lasts 14 * 66.7 μs ≈ 0.934 ms, while a slot at 120 kHz spacing lasts 14 * 8.33 μs ≈ 0.117 ms. This rapid slot structure is crucial for achieving the low latency targets of 5G.
Table of 5G Numerology Parameters
The following table summarizes the key parameters of 5G NR numerology as derived from the provided source material. This table illustrates how the fundamental parameters scale with the chosen subcarrier spacing.
| Subcarrier Spacing (kHz) | Symbol Duration (μs) | Cyclic Prefix Duration (μs) | Max. Nominal System Bandwidth (MHz) | Symbols per Slot | Slots per Subframe | Slots per Frame |
|---|---|---|---|---|---|---|
| 15 | 66.7 | 4.7 | 50 | 14 | 1 | 10 |
| 30 | 33.3 | 2.3 | 100 | 14 | 2 | 20 |
| 60 | 16.7 | 1.2 (Normal), 4.13 (Extended) | 100 (sub-6 GHz), 200 (mmwave) | 14 (Normal), 12 (Extended) | 4 | 40 |
| 120 | 8.33 | 0.59 | 400 | 14 | 8 | 80 |
| 240 | 4.17 | 0.29 | 400 | 14 | 16 | 160 |
This table provides a clear overview of the scaling relationships within the 5G numerology. It shows that as subcarrier spacing doubles, the symbol duration is halved, and the number of slots per subframe and per frame doubles. This systematic scaling allows network operators to select the most appropriate numerology for their specific deployment needs, ensuring optimal performance across a wide range of frequencies and applications.
5G Frequency Ranges and Application Scenarios
The 5G NR standard supports two primary frequency ranges, each with its own set of characteristics and preferred numerologies.
- Frequency Range 1 (FR1): This range encompasses frequencies from 450 MHz to 6 GHz. It is the backbone of mainstream 5G deployment, providing a balance of coverage and capacity. For FR1, subcarrier spacings of 15 kHz, 30 kHz, and 60 kHz are commonly used. The lower spacings are suitable for wide-area coverage, while 60 kHz can be used to support higher data rates or reduce latency in dense urban environments.
- Frequency Range 2 (FR2): This range includes frequencies from 24.25 GHz to 52.6 GHz, commonly known as the millimeter-wave (mmwave) bands. FR2 offers immense bandwidth, enabling very high data rates. However, signals in this range are more susceptible to blockage and have a shorter propagation range. To mitigate these challenges, larger subcarrier spacings such as 120 kHz and 240 kHz are used. These wider spacings are more robust against Doppler shift and phase noise, which are more pronounced at higher frequencies. Furthermore, FR2 deployments heavily rely on beamforming techniques to direct signals and overcome path loss.
These frequency ranges are designed to support a diverse set of usage scenarios defined by the 3GPP:
- Enhanced Mobile Broadband (eMBB): This scenario focuses on delivering high data rates for applications like high-definition video streaming, virtual reality, and fixed wireless access. It requires a combination of high capacity and wide coverage, leveraging both FR1 and FR2.
- Massive Machine-Type Communication (mMTC): This scenario targets the connection of a very large number of low-power, low-data-rate devices, such as sensors in the Internet of Things (IoT). It prioritizes spectral efficiency and deep indoor coverage, often using lower subcarrier spacings.
- Ultra-Reliable and Low-Latency Communication (URLLC): This scenario is critical for mission-critical applications like autonomous vehicles, remote surgery, and industrial automation. It demands extremely high reliability and very short communication delays. The flexible slot structure of 5G numerology, allowing for mini-slots and rapid scheduling, is key to meeting the stringent requirements of URLLC.
The 5G numerology table is not merely a technical specification; it is the enabler of this diverse ecosystem. By providing a flexible framework for defining the physical layer, it allows a single network infrastructure to be dynamically configured to serve vastly different needs, from streaming 4K video to controlling a fleet of autonomous drones. This adaptability is a cornerstone of the 5G vision.
Conclusion
The term "numerology" in the context of 5G wireless communication refers to a comprehensive set of physical layer parameters that define the waveform and resource structure of the network. Governed by the standards set by the 3GPP, this technical numerology provides the flexibility necessary to support a wide range of frequency bands (FR1 and FR2) and diverse application scenarios (eMBB, mMTC, URLLC). The core parameters—subcarrier spacing, symbol duration, Cyclic Prefix, and slot structure—are intricately linked, allowing system designers to make critical trade-offs between data rate, latency, robustness, and spectral efficiency. The detailed 5G numerology table, with its scaling values for different subcarrier spacings from 15 kHz to 240 kHz, is the blueprint for the efficient and versatile operation of 5G NR networks, paving the way for the next generation of connected devices and services.