The provided source material exclusively addresses technical specifications of 5G New Radio (NR) telecommunications, specifically focusing on the principles of Orthogonal Frequency Division Multiplexing (OFDM), numerology (μ), subcarrier spacing (Δf), and resource element allocation. These sources detail how 5G technology utilizes scalable numerology to support diverse use cases ranging from enhanced mobile broadband (eMBB) to ultra-reliable low-latency communication (URLLC) and massive machine-type communication (mMTC). The core concept relies on variable subcarrier spacing, calculated as Δf = 15 kHz × 2μ, which allows for flexible frame structures, optimized spectral efficiency, and adaptation to different frequency ranges (FR1 and FR2). The sources describe the relationship between bandwidth, subcarriers, and resource blocks, as well as the impact of numerology on slot duration and symbol length.
Understanding 5G NR Numerology
Numerology in the context of 5G refers to the various configurations of subcarrier spacing and other parameters designed to meet specific performance and deployment requirements. According to the source data, the term "numerology" encapsulates the flexibility and scalability of the system, allowing it to cater to a wide range of use cases. The primary characteristic defining these different numerologies is the subcarrier spacing (Δf), which is a critical factor in defining symbol duration and cyclic prefix length.
The subcarrier spacing is determined by the formula: Δf = 15 kHz × 2μ, where μ is an integer representing the numerology index. The 5G standard defines multiple numerologies, each suited to specific deployment scenarios and service requirements. The flexibility of the system is highlighted by its ability to support multiple numerologies simultaneously within the same frame structure. This scalability allows low-latency services to utilize higher numerologies (resulting in more slots per frame) while coverage-oriented services utilize lower numerologies.
Subcarrier Spacing and Resource Elements
In 5G NR, communication between the base station (gNB) and user equipment (UE) is based on Orthogonal Frequency Division Multiplexing (OFDM). This modulation scheme divides the configured spectrum into numerous closely spaced subcarriers that communicate simultaneously. These subcarriers are orthogonal (non-overlapping), providing separation and high spectral efficiency while mitigating multipath fading.
A Resource Element (RE) is defined by one subcarrier in the frequency domain and one symbol in the time domain. The subcarrier spacing directly determines the bandwidth of the Resource Element, while the duration of the symbol (excluding the cyclic prefix) is inversely proportional to the subcarrier spacing. Multiple subcarriers and symbols create a grid of Resource Elements, which is fundamental to mapping physical channels and signals. Each 5G NR carrier is divided into Resource Blocks (RBs), where a Resource Block contains 12 subcarriers.
The relationship between bandwidth and subcarriers is expressed as: Total subcarriers = Bandwidth / Subcarrier spacing. As Δf increases, the total number of subcarriers decreases while maintaining the same bandwidth. For example, in a 100 MHz channel: - At 15 kHz spacing, there are approximately 6600 subcarriers. - At 60 kHz spacing, there are approximately 1800 subcarriers.
The Flexible Frame Structure
The frame structure of 5G NR is implemented to support multiple numerologies at the same time. A frame has a duration of 10 ms and is composed of 10 subframes, each having a 1 ms duration. Each subframe consists of slots, and each slot can have either 14 (normal CP) or 12 (extended CP) OFDM symbols. While most spacing options support 14 OFDM symbols, 60 kHz spacing supports both normal and extended CP types.
The number of slots per subframe varies by numerology (μ): - μ = 0: 1 slot per subframe - μ = 1: 2 slots per subframe - μ = 2: 4 slots per subframe - μ = 3: 8 slots per subframe - μ = 4: 16 slots per subframe
The number of slots per frame is ten times the number of slots per subframe. For instance, for μ = 2, there are 40 slots per frame. This scalable mechanism allows the system to prioritize low-latency services using higher numerologies or coverage-oriented services using lower numerologies.
Specific Numerologies and Use Cases
The 5G standard defines five primary numerologies characterized by their subcarrier spacing and associated slot durations. These variations are tailored to specific operational needs and frequency ranges.
Table: 5G NR Numerologies and Characteristics
| Numerology (μ) | Subcarrier Spacing (Δf) | Slot Duration (ms) | Symbol Duration (µs) | CP Duration (µs) | Typical Use Case |
|---|---|---|---|---|---|
| 0 | 15 kHz | 1.0 | 66.7 | 4.7 | Compatible with LTE, low frequency bands, Massive IoT (mMTC) |
| 1 | 30 kHz | 0.5 | 33.3 | 2.3 | Sub 6 GHz, eMBB (Enhanced Mobile Broadband) |
| 2 | 60 kHz | 0.25 | 16.7 | 1.2 (Normal), 4.13 (Extended) | mmWave, low latency |
| 3 | 120 kHz | 0.125 | 8.33 | 0.59 | mmWave, ultra-low latency (URLLC) |
| 4 | 240 kHz | 0.0625 | 4.17 | 0.29 | Very High Frequency mmWave |
Enhanced Mobile Broadband (eMBB)
For applications requiring high throughput, such as streaming and virtual reality, a bandwidth of 100 MHz with 30 kHz spacing (μ=1) is typically utilized. This configuration supports high data rates required for data-intensive applications.
Ultra-Reliable Low-Latency Communication (URLLC)
URLLC applications, such as autonomous systems, require extremely low latency. This is achieved using spacing of 60 kHz (μ=2) or 120 kHz (μ=3). The shorter slot durations associated with these higher numerologies significantly reduce transmission delay.
Massive IoT (mMTC)
Massive Machine-Type Communication involves low-power sensors requiring extended coverage and battery life. A subcarrier spacing of 15 kHz (μ=0) is suitable for this use case, providing larger coverage areas and supporting extended battery life for IoT sensors.
Resource Block and Grid Definitions
The number of Resource Blocks (RBs) varies depending on the numerology and subcarrier spacing. The 5G NR system utilizes 4096 FFT points, consisting of 3300 data subcarriers for a maximum bandwidth of 400 MHz. The grid of Resource Elements (REs) is defined relative to the numerology, ensuring that physical channels and signals are mapped correctly across the frequency and time domains.
Benefits of OFDM in 5G NR
The implementation of OFDM in 5G NR provides several key benefits derived from the scalable numerology: - High Spectral Efficiency: Minimal guard bands between subcarriers allow for efficient use of the spectrum. - Multipath Resilience: The system effectively manages inter-symbol interference, which is crucial for maintaining signal integrity in varied environments. - Flexible Configuration: The ability to adjust subcarrier spacing (Δf) allows the system to adapt to different deployment scenarios and service requirements. - Ability to Handle Wide Bandwidths: The technology functions well across both FR1 (sub-6 GHz) and FR2 (mmWave) systems, supporting the diverse needs of 5G connectivity.
Conclusion
The concept of 5G NR subcarriers and numerology (μ) underlines the flexibility and scalability of 5G technology. By utilizing a scalable frame structure that supports multiple numerologies simultaneously, 5G can dynamically allocate resources to meet the specific performance needs of diverse applications. From low-power IoT sensors using 15 kHz spacing to ultra-low latency autonomous systems using 120 kHz spacing, the numerology framework ensures that the network can optimize spectral efficiency, latency, and coverage based on the specific use case and frequency range.