The introduction of 5G New Radio (NR) technology brings numerous advancements to mobile communication, one of which is the detailed framework for numerology and resource elements as specified in 3GPP TS 38.211. This technical article explores these concepts, their importance, and their application in 5G NR, providing a comprehensive understanding of how they shape the 5G landscape.
Numerology in 5G NR
Numerology in 5G NR defines the subcarrier spacing in the frequency domain. According to 3GPP TS 38.211, there are five different numerologies specified with subcarrier spacings of 15 kHz, 30 kHz, 60 kHz, 120 kHz, and 240 kHz. Each numerology impacts the bandwidth and duration of a single Resource Element (RE).
Subcarrier Spacing and Resource Elements
A Resource Element 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.
For instance, at a 15 kHz subcarrier spacing:
Bandwidth: 15 kHz
Duration: 1/15 kHz=0.067 ms1/15 \, \text{kHz} = 0.067 \, \text{ms}1/15kHz=0.067ms
At a 30 kHz subcarrier spacing:
Bandwidth: 30 kHz
Duration: 1/30 kHz=0.033 ms1/30 \, \text{kHz} = 0.033 \, \text{ms}1/30kHz=0.033ms
This relationship is illustrated in Figure 1.
Resource Element Grid
Multiple subcarriers in the frequency domain and multiple symbols in the time domain create a grid of Resource Elements. This grid is fundamental to mapping physical channels and signals. Figure 2 demonstrates a Resource Element grid for a 15 kHz subcarrier spacing.
Modulation and Transmission
Each Resource Element can carry one modulation symbol, which can represent different amounts of data based on the modulation scheme:
QPSK: 2 bits per symbol
16QAM: 4 bits per symbol
64QAM: 6 bits per symbol
256QAM: 8 bits per symbol
The use of multiple subcarriers and symbols results in the modulation and summing of these subcarriers, a process facilitated by the Inverse Fast Fourier Transform (IFFT). Figure 3 illustrates this process.
Combining Numerologies
5G allows the combination of different numerologies within a single symbol duration, enhancing its flexibility to support diverse deployment scenarios and end-user applications. For example, subcarrier spacings of 15 kHz and 30 kHz can be combined, but not 15 kHz and 120 kHz. Figure 4 illustrates this concept.
Deployment Scenarios
Different numerologies suit various deployment scenarios:
Larger propagation delay spreads: Use lower subcarrier spacings for longer symbol durations and cyclic prefixes.
High mobility (e.g., high-speed trains): Use higher subcarrier spacings to mitigate Doppler frequency offsets.
Low latency applications: Use higher subcarrier spacings for shorter symbol durations, facilitating quick data transmission and acknowledgment.
Numerologies and Cyclic Prefixes
The full set of numerologies is available with the normal cyclic prefix, and 3GPP has also specified an extended cyclic prefix for the 60 kHz subcarrier spacing. Table 1 outlines the key characteristics of numerologies with the normal cyclic prefix.
μ | Subcarrier Spacing | Slots per 10 ms Radio Frame | Slots per 1 ms Subframe | Symbols per Slot | Symbol Duration (μs) | Slot Duration (μs) | Operating Bands | Expected Use Case |
0 | 15 kHz | 10 | 1 | 14 | 71.875 | 1000 | Frequency Range 1 | eMBB, URLLC |
1 | 30 kHz | 20 | 2 | 14 | 35.677 | 500 | Frequency Range 1 | eMBB, URLLC |
2 | 60 kHz | 40 | 4 | 14 | 17.839 | 250 | Frequency Range 2 | eMBB, URLLC |
3 | 120 kHz | 80 | 8 | 14 | 8.919 | 125 | Frequency Range 2 | eMBB, URLLC |
4* | 240 kHz | 160 | 16 | 14 | 4.460 | 62.5 | Synchronization Signal/PBCH Blocks | Not used for data transfer |
Table 2 presents the characteristics of the extended cyclic prefix for the 60 kHz subcarrier spacing.
μ | Subcarrier Spacing | Slots per 10 ms Radio Frame | Slots per 1 ms Subframe | Symbols per Slot | Symbol Duration (μs) | Slot Duration (μs) | Operating Bands | Expected Use Case |
2 | 60 kHz | 40 | 4 | 12 | 20.833 | 250 | Frequency Ranges 1 & 2 | eMBB, URLLC |
Conclusion
The 3GPP TS 38.211 specification provides a robust framework for understanding numerology and resource elements in 5G NR. This framework enables flexible deployment scenarios and diverse end-user applications, ensuring that 5G networks are capable of meeting the varied demands of modern communication. By leveraging these detailed specifications, the telecommunications industry can achieve a seamless and efficient rollout of 5G technology.
References
3GPP. (n.d.). TS 38.211 V15.2.0: NR; Physical channels and modulation. Retrieved from 3GPP
3GPP. (n.d.). TS 38.101-1 V15.2.0: NR; User Equipment (UE) radio transmission and reception; Part 1: Range 1 Standalone. Retrieved from 3GPP
3GPP. (n.d.). TS 38.300 V15.2.0: NR; NR and NG-RAN Overall Description; Stage 2. Retrieved from 3GPP
3GPP. (n.d.). TS 38.213 V15.2.0: NR; Physical layer procedures for control. Retrieved from 3GPP
For further reading and access to the complete list of specifications, visit the 3GPP website at www.3gpp.org.
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