In wireless communications, spectrums are always scarce resources. Generally, low-frequency spectrums are preferred resources and feature small bandwidths. However, most of them have been occupied by communications systems of previous generations. Considering the large bandwidth requirements of 5G, 3rd Generation Partnership Project (3GPP) has planned both low-frequency spectrums that have not been allocated by the International Telecommunication Union (ITU) and high-frequency spectrums for 5G. Therefore, there are two types of 5G NR spectrums: Frequency Range 1 (FR1) and Frequency Range 2 (FR2).
- FR1: primary 5G frequency band, also called sub-6 GHz. Its frequency range is generally below 6 GHz and that is why it is also called the 5G low frequency band. Since protocols are constantly evolving, the highest frequency of FR1 has been extended to 7125 MHz in the latest 3GPP TS 38.104. Even though this exceeds 6 GHz, the nomenclature has not changed and FR1 is still called the sub-6 GHz frequency band. In FR1, frequency bands below 3 GHz are also referred to as sub-3 GHz frequency bands, while the remainder as the C-band. Most spectrum resources below 3 GHz have been occupied by communications systems of previous generations, so only a few countries and regions have planned continuous spectrums with a large bandwidth for 5G NR in this spectrum range. That said, for most countries, the C-band is not occupied by existing communications systems, so continuous spectrums in this band with a large bandwidth can be allocated to 5G NR. Therefore, the ITU World Radiocommunication Conference 2015 (WRC-15) preliminarily concluded that the C-band will likely become the globally standard 5G frequency band.
- FR2: extended 5G frequency band, also called the millimeter wave (mmWave) band or 5G high frequency band. The latest 3GPP TS 38.104 stipulates that FR2 ranges from 24 GHz to 52 GHz. However, 3GPP working groups have discussed the possibility of planning higher frequency spectrum resources for 5G NR as protocols continue to evolve. WRC-19 proposed that the 5G mmWave frequency band be extended to 71 GHz.
Figure below shows the 5G NR spectrums.
FR1 and FR2 refer to the overall large spectrum ranges of 5G NR. However, some spectrum resources in each have already been occupied by other communications systems, and the actual availability may vary by country. Therefore, 3GPP evaluates the specific spectrum resource usage and future planning for each country and divides the spectrum resources of FR1 and FR2 into several frequency bands. This helps operators select the appropriate frequency bands based on spectrum resource availability when they deploy 5G networks in different countries. However, before we delve into frequency band division, it is important to understand duplex modes.
Duplex Mode.
The opposite of duplex is simplex. In simplex mode, data can be transmitted only in one direction. One of the two communication parties is fixed as the transmit end, and the other the receive end. Duplex means that each party in communication can either be the sender or the receiver. If a party cannot receive data when sending data, or cannot send data when receiving data, the communication is in half-duplex mode. If a party can receive and send data simultaneously, the communication is in full-duplex mode.
Since LTE, air interface resources are time-frequency resources.
- If a base station and a UE use different frequency resources for uplink and downlink communication, they work in frequency division duplex (FDD) mode.
- If a base station and a UE use the same frequency resource but different time domain resources for uplink and downlink communication, they work in TDD mode.
The duplex modes of 5G NR inherit LTE design. However, from the perspective of system division, LTE emphasizes different duplex modes, such as LTE TDD and LTE FDD. On the contrary, due to flexible slot types and formats, the type of duplex mode is rarely mentioned at the system level in 5G.
Keep in Mind!
For a UE in an LTE TDD or a 5G NR TDD system, although resources used for reception and transmission are distinguished in the time domain, the UE can simultaneously send and receive data in terms of radio frame usage or actual user experience. Therefore, TDD is generally considered a full-duplex system.
5G NR Frequency Bands.
Spectrum resources are divided into several frequency bands in both LTE and 5G NR. In 5G NR, these frequency bands are numbered in the format of “n+digit” and the duplex mode of each frequency band must be specified as any of the following:
- FDD: frequency division duplex
- TDD: time division duplex
- SDL: supplementary downlink. An SDL band only supports transmission from gNodeBs to UEs.
- SUL: supplementary uplink. An SUL band only supports transmission from UEs to gNodeBs.
Table 1 and Table 2 list the frequency bands of FR1 and FR2 defined in 3GPP TS 38.104. FR1 includes 45 frequency bands and FR2 includes four frequency bands. All frequency bands in FR2 are in TDD mode because:
- FR2 frequency bands are high frequency bands with poor coverage capabilities, so improving 5G NR coverage requires many antenna units together with beamforming. To use beamforming, the gNodeB must obtain the channel state information (CSI) of UEs, which may require configuring many downlink reference signals for UEs. Unlike FDD, the uplink and downlink in TDD use the same frequency band and the reciprocity between the uplink and downlink allows the gNodeB to obtain the CSI from UEs’ measurement reports in the uplink, reducing downlink radio resource consumption.
- The minimum frequency bandwidth in FR2 is around 1 GHz. If a high frequency band is used in the downlink as an FDD band, another frequency band with the same bandwidth must be used in the uplink, posing difficulties to network planning. Moreover, the maximum carrier bandwidth of frequency bands in FR2 is 400 MHz, facilitating transmission of a large amount of data, especially in hotspot areas. Services requiring such a large carrier bandwidth are generally asymmetric (with the downlink traffic being greater than the uplink traffic) and the bandwidth requirement in the uplink is lower than in the downlink. TDD supports dynamic uplink and downlink resource allocation, which is more suitable for asymmetric service scenarios. Compared with FDD, TDD can reduce the waste of uplink bandwidth resources when the uplink traffic volume is small.
Table 1 – Frequency bands of FR1.
| NR Operating Band | UL Operating Band FUL_low – FUL_high | DL Operating Band FDL_low – FDL_high | Duplex Mode |
|---|---|---|---|
| n1 | 1920 MHz–1980 MHz | 2110 MHz–2170 MHz | FDD |
| n2 | 1850 MHz–1910 MHz | 1930 MHz–1990 MHz | FDD |
| n3 | 1710 MHz–1785 MHz | 1805 MHz–1880 MHz | FDD |
| n5 | 824 MHz–849 MHz | 869 MHz–894 MHz | FDD |
| n7 | 2500 MHz–2570 MHz | 2620 MHz–2690 MHz | FDD |
| n8 | 880 MHz–915 MHz | 925 MHz–960 MHz | FDD |
| n12 | 699 MHz–716 MHz | 729 MHz–746 MHz | FDD |
| n14 | 788 MHz–798 MHz | 758 MHz–768 MHz | FDD |
| n18 | 815 MHz–830 MHz | 860 MHz–875 MHz | FDD |
| n20 | 832 MHz–862 MHz | 791 MHz–821 MHz | FDD |
| n25 | 1850 MHz–1915 MHz | 1930 MHz–1995 MHz | FDD |
| n28 | 703 MHz–748 MHz | 758 MHz–803 MHz | FDD |
| n29 | N/A | 717 MHz–728 MHz | SDL |
| n30 | 2305 MHz–2315 MHz | 2350 MHz–2360 MHz | FDD |
| n34 | 2010 MHz–2025 MHz | 2010 MHz–2025 MHz | TDD |
| n38 | 2570 MHz–2620 MHz | 2570 MHz–2620 MHz | TDD |
| n39 | 1880 MHz–1920 MHz | 1880 MHz–1920 MHz | TDD |
| n40 | 2300 MHz–2400 MHz | 2300 MHz–2400 MHz | TDD |
| n41 | 2496 MHz–2690 MHz | 2496 MHz–2690 MHz | TDD |
| n48 | 3550 MHz–3700 MHz | 3550 MHz–3700 MHz | TDD |
| n50 | 1432 MHz–1517 MHz | 1432 MHz–1517 MHz | TDD |
| n51 | 1427 MHz–1432 MHz | 1427 MHz–1432 MHz | TDD |
| n65 | 1920 MHz–2010 MHz | 2110 MHz–2200 MHz | FDD |
| n66 | 1710 MHz–1780 MHz | 2110 MHz–2200 MHz | FDD |
| n70 | 1695 MHz–1710 MHz | 1995 MHz–2020 MHz | FDD |
| n71 | 663 MHz–698 MHz | 617 MHz–652 MHz | FDD |
| n74 | 1427 MHz–1470 MHz | 1475 MHz–1518 MHz | FDD |
| n75 | N/A | 1432 MHz–1517 MHz | SDL |
| n76 | N/A | 1427 MHz–1432 MHz | SDL |
| n77 | 3300 MHz–4200 MHz | 3300 MHz–4200 MHz | TDD |
| n78 | 3300 MHz–3800 MHz | 3300 MHz–3800 MHz | TDD |
| n79 | 4400 MHz–5000 MHz | 4400 MHz–5000 MHz | TDD |
| n80 | 1710 MHz–1785 MHz | N/A | SUL |
| n81 | 880 MHz–915 MHz | N/A | SUL |
| n82 | 832 MHz–862 MHz | N/A | SUL |
| n83 | 703 MHz–748 MHz | N/A | SUL |
| n84 | 1920 MHz–1980 MHz | N/A | SUL |
| n86 | 1710 MHz–1780 MHz | N/A | SUL |
| n89 | 824 MHz–849 MHz | N/A | SUL |
| n90 | 2496 MHz–2690 MHz | 2496 MHz–2690 MHz | TDD |
| n91 | 832 MHz–862 MHz | 1427 MHz–1432 MHz | FDD |
| n92 | 832 MHz–862 MHz | 1432 MHz–1517 MHz | FDD |
| n93 | 880 MHz–915 MHz | 1427 MHz–1432 MHz | FDD |
| n94 | 880 MHz–915 MHz | 1432 MHz–1517 MHz | FDD |
| n95 | 2010 MHz–2025 MHz | N/A | SUL |
Table 3-2 Frequency bands of FR2
| NR Operating Band | UL Operating Band FUL_low – FUL_high | DL Operating Band FDL_low – FDL_high | Duplex Mode |
|---|---|---|---|
| n257 | 26500 MHz–29500 MHz | 26500 MHz–29500 MHz | TDD |
| n258 | 24250 MHz–27500 MHz | 24250 MHz–27500 MHz | TDD |
| n260 | 37000 MHz–40000 MHz | 37000 MHz–40000 MHz | TDD |
| n261 | 27500 MHz–28350 MHz | 27500 MHz–28350 MHz | TDD |
References.
- 3GPP TS 38.101-2, User Equipment (UE) radio transmission and reception; Part 1: Range 2 Standalone (Release 16)
- 3GPP TS 38.101-1, User Equipment (UE) radio transmission and reception; Part 1: Range 1 Standalone (Release 16)
- 3GPP TS 38.300, NR and NG-RAN Overall Description; Stage 2 (Release 16)
- 3GPP TS 38.104, Base Station (BS) radio transmission and reception (Release 16)
- 3GPP TS 38.213, Physical layer procedures for control (Release 16)
- 3GPP TS 38.211, Physical channels and modulation (Release 16)
- 3GPP TS 36.213, Physical layer procedures (Release 16)
- 3GPP TS 36.211, Physical channels and modulation (Release 14)
- 3GPP TR 38.912 (Release 15)
- 3GPP TR 38.802, Physical Layer Aspects (Release 14).
Interview Questions asked about 5G Frequency Domain Resources in telecom sector.
Q.1 What are the functions of the synchronization raster?
Q.2 Why synchronization raster is introduced to 5G NR?
Q.3 What is a bandwidth part (BWP)?
Q.4 Why are BWPs introduced in 5G NR?
Q.5 How does a UE obtain its BWP information from the network?
Q.6 What are the basic frequency domain resources in 5G NR?
Q.7 How do frequency domain resources differ from LTE?
Q.8 What are the duplex modes of the 5G NR frequency bands?
Q.9 Why does FR2 only operate in time division duplex (TDD)?