What is 5G NR-U or New Radio-Unlicensed?

5G New Radio-Unlicensed (NR-U) is a 3GPP Release 16 mode of operation that provides the necessary technology for cellular operations to integrate unlicensed spectrum into 5G networks. NR-U enables both uplink and downlink operation in unlicensed bands supporting 5G features like wideband carriers, flexible numerologies, dynamic TDD, beamforming, and dynamic scheduling/HARQ timing etc.

NR-U supports deployment in 3 modes, depending on how it is used for the user plane (which carries the network user traffic) and the control plane (which carries signaling traffic):

• Carrier Aggregation, where the unlicensed spectrum is used only to increase downstream user plane capacity. Control plane data is transported over the licensed spectrum only.
• Dual Connectivity, which supports both upstream and downstream user plane traffic over the unlicensed spectrum. This is also designed for traffic offload and not coverage so control plane traffic is transported only over the licensed spectrum.
• Standalone, which is the first 3GPP-defined mode of operation that relies solely on the unlicensed spectrum for control and user plane traffic.

NR-U’s standalone mode eliminates any dependency on licensed network operators and is open for implementation by private enterprises, managed service providers or network systems integrators. This enables private 5G deployments supporting new consumer and Industry 4.0 applications to gain access to secure, low-latency, reliable, high-bandwidth connectivity to densely populated endpoints. While the carrier aggregation and dual connectivity modes are designed to operate in the 5 GHz spectrum, the NR-U standalone mode has been built for all sub-7 GHz mid-band ranges plus high-band frequencies in the 57 to 71 GHz ranges that are opening up for unlicensed use around the globe. Support for these mmWave bands is defined within 3GPP release 17 specifications.

The primary concern of operating in NR-U is operating in the highly utilized 5 GHz bands while ensuring harmonious coexistence with other mobile technologies like Wi-Fi. For this 5G NR Radio access network (RAN) is also introduced for NR-U bands which means that while NR-U employs the 5G NR physical (PHY) layer to leverage 5G’s evolutionary benefits, the medium access control (MAC) layer protocols for processes such as channel access have been modified to align with Wi-Fi. This means that NR-U’s impact on existing Wi-Fi networks is equivalent to adding another Wi-Fi access point. NR-U follows the same contention-based listen-before-talk (LBT) protocol employed in 802.11 to ensure equal access to available channels. This is referred to as asynchronous NR-U operation and does limit some of the benefits of 5G NR, such as the ability to support ultra-reliable low-latency communication (URLLC).

Even more opportunities for better spectral efficiencies have opened up as new, less populated, frequency ranges become available to NR-U. In the US, EU and South Korea, the 5.925 GHz to 7.125 GHz (or 6 GHz) frequency range is now being opened-up for unlicensed devices. In the US, the Federal Communications Commission (FCC) allows unlicensed use of the 6 GHz band for low power (30 dBm) indoor applications and outdoor operation at the same levels as 5 GHz systems (36 dBm) with the compulsory use of an automated frequency control (AFC) system, like the spectrum access system (SAS) employed in the citizens broadband radio service (CBRS). This is to prevent interference with existing earth-to-space satellites and point-to-point microwave links also operating on these wavelengths.

Even though the 6 GHz band is used by some technologies including the new Wi-Fi 6, It is considered a greenfield spectrum because of the abundance of the available spectrum together with the absence of any incumbency and the natural isolation of signals owing to their low propagation rates through the air and physical structures, all of which means interference will be negligible. This enables NR-U operating in or above the 6 GHz frequency range to be free of the strict LBT protocols adopted for harmonious coexistence in the 5 GHz bands. This permits rapid access to transmission channels in support of low-latency automation and IoT applications.