The provided source material focuses exclusively on the technical specifications of 5G New Radio (NR) numerology and channel bandwidth. It details the relationship between numerology index, subcarrier spacing, resource blocks, and bandwidth calculations as defined by 3GPP standards. The following article synthesizes this technical information to explain how 5G networks adapt to various frequency bands and deployment scenarios.
Fundamentals of 5G Numerology
In 5G NR, numerology (μ) is the defining parameter for subcarrier spacing (Δf). Unlike LTE, which utilized a fixed subcarrier spacing of 15 kHz, 5G employs a scalable approach. The relationship is defined by the formula:
Δf = 15 kHz × 2^μ
This scalable numerology allows the network to adjust the physical layer parameters to suit specific frequency ranges and use cases. The source material identifies five distinct numerologies, ranging from μ = 0 to μ = 4, corresponding to subcarrier spacings of 15 kHz, 30 kHz, 60 kHz, 120 kHz, and 240 kHz.
The choice of numerology impacts several critical aspects of the signal: * Symbol Duration: As μ increases, the subcarrier spacing doubles, and the symbol duration is halved. This reduction in symbol duration is crucial for achieving ultra-low latency in high-frequency deployments. * Cyclic Prefix (CP): The duration of the cyclic prefix also scales with numerology. While most numerologies support normal CP, μ = 2 (60 kHz) supports both normal and extended CP types. Extended CP is utilized to mitigate severe multipath delay spread in specific environments.
The structure of the 5G frame is also dependent on numerology. A 5G frame has a duration of 10 ms, consisting of 10 subframes of 1 ms each. Each subframe contains a variable number of slots depending on μ. For instance, μ = 0 yields 1 slot per subframe, while μ = 3 yields 4 slots per subframe. This flexibility allows for faster transmission of data in higher numerologies.
Resource Elements and Bandwidth Calculation
The foundation of 5G resource allocation is the Resource Element (RE), defined by one subcarrier in the frequency domain and one symbol in the time domain. A Resource Block (RB) consists of 12 subcarriers. The total bandwidth occupied by an OFDM signal is calculated using the formula:
BW = 12 × N_RB × Δf
Where N_RB is the number of resource blocks.
The source material provides a detailed table outlining the minimum and maximum channel bandwidths for each numerology. The number of resource blocks generally ranges from a minimum of 24 to a maximum of 275 for numerologies μ = 0 through μ = 3. However, for μ = 4 (240 kHz), the maximum number of resource blocks drops to 138. This limitation is due to the larger subcarrier spacing restricting the number of subcarriers that fit within the available spectrum.
Minimum and Maximum Channel Bandwidth
The concept of minimum and maximum channel bandwidth is essential for network planning and spectrum licensing. The minimum bandwidth represents the smallest configuration that accommodates the minimum number of resource blocks (24 RBs), suitable for narrowband applications or tight spectrum availability. The maximum bandwidth represents the largest configuration the system can manage for a specific numerology, utilized in high-capacity deployments to achieve peak data rates.
The relationship between numerology and bandwidth is approximately linear regarding doubling. For example, the maximum bandwidth for μ = 0 (15 kHz) is 49.5 MHz, while for μ = 1 (30 kHz), it is 99.2 MHz. This scaling allows operators to utilize available spectrum efficiently across different frequency bands.
Trade-offs: Coverage, Latency, and Throughput
The flexibility of 5G numerology introduces a trade-off between coverage, capacity, and latency.
- Low Numerologies (μ = 0, 1): These utilize wider symbol durations (66.67 µs and 33.33 µs respectively). The longer symbol duration provides robustness against fading and interference, making them ideal for wide-area coverage in Frequency Range 1 (FR1), specifically low-band and mid-band frequencies (sub-6 GHz). They offer higher coverage but higher latency compared to higher numerologies.
- High Numerologies (μ = 3, 4): These utilize shorter symbol durations (8.33 µs and 4.17 µs). This significantly reduces latency, making them suitable for ultra-reliable low-latency communications (URLLC) and high-throughput applications. These numerologies are primarily used in Frequency Range 2 (FR2), the mmWave spectrum. However, the short symbol duration makes the signal more susceptible to interference and limits coverage range, requiring clear line-of-sight conditions.
Practical Deployment: C-Band Example
A practical application of these principles is seen in C-band 5G deployments (around 3.5 GHz). This frequency band typically utilizes numerology μ = 1 (30 kHz subcarrier spacing) with a channel bandwidth of 100 MHz. According to the provided data, the maximum resource blocks for μ = 1 is 275, which corresponds to a bandwidth of 99.2 MHz. This alignment confirms the standardization of 100 MHz carriers for C-band, enabling peak speeds over 1 Gbps while maintaining a reasonable cell radius for urban environments.
Importance for Network Optimization
Understanding minimum and maximum channel bandwidth is critical for several operational aspects: 1. Spectrum Licensing: Operators must plan deployments within licensed frequency ranges, ensuring their bandwidth configurations comply with regulatory limits. 2. Carrier Aggregation: Knowledge of bandwidth limits helps determine how many component carriers can be combined to achieve gigabit speeds. 3. User Equipment (UE) Capability: Devices must support specific bandwidth classes (e.g., up to 100 MHz for FR1 or 400 MHz for FR2) to function correctly on the network. 4. Network Optimization: Engineers can fine-tune the network by selecting the appropriate numerology and bandwidth to balance latency, coverage, and throughput goals.
Conclusion
5G NR numerology provides the necessary flexibility to support diverse deployment scenarios, from wide-area coverage using low-band frequencies to ultra-high throughput using mmWave. By adjusting the subcarrier spacing and bandwidth configuration, network operators can optimize for specific performance metrics such as latency or coverage. The strict definitions provided by 3GPP TS 38.211 ensure standardization across the global telecommunications industry, facilitating the rollout of robust and efficient 5G networks.