5G New Radio

5G defines a new radio interface called 5G New Radio (NR). Rather than being something new, it should be seen as an evolution of LTE technology. In fact, the term Next Generation Radio Access Network (NG-RAN) is commonly used and it covers both 5G NR and LTE/E-UTRA radio access.

5G attempts to address many new use cases not possible in earlier generations. 5G NR plays an important role in fulfilling these new cases. All layers of the 5G NR protocol stack are enhanced but perhaps most changes are within PHY.

While there are many 3GPP specifications that define 5G NR, beginners can start with TS 38.300 and TS 38.401 that give high-level descriptions.


  • Which are the 5G NR technical enablers for achieving 5G use cases?
    Key features and benefits of 5G NR. Source: Nokia Networks, via Ghosh 2018, slide 2.
    Key features and benefits of 5G NR. Source: Nokia Networks, via Ghosh 2018, slide 2.

    The three broad 5G use cases supported by 5G NR are Enhanced Mobile Broadband (eMBB), Massive Machine-Type Communications (mMTC) and Ultra-Reliable Low-Latency Communications (URLLC).

    5G NR spans spectra from sub-GHz to mmWave bands. This enables deployments of macro cells to picocells. Both licensed and unlicensed bands are allowed. Wide bandwidths at mmWave bands enable eMBB. Multiple bands can be combined to offer higher data rates and boost capacity.

    For URLLC, reliability is improved via multi-antenna transmission, multiple carriers and packet duplication. Latency is reduced by mini-slot transmission, grant-free uplink access, and eMBB resource pre-emption. Control and reference signals appear at the start of a slot.

    To cater to wide range of bands and deployments, OFDM Sub-Carrier Spacing (SCS) is flexible while maintaining time-domain alignment. As SCS goes up, the slot duration shrinks. For example, wider SCS might suit URLLC and a narrower SCS for MBB/mMTC.

    There are many ways to aggregate slots with guard periods between uplink and downlink. Thus, we can have short transmissions for URLLC and longer ones for eMBB.

  • What are the key design principles behind 5G NR?
    5G NR adopts ultra-lean design. Source: Nokia Networks, via Ghosh 2018, slide 6.
    5G NR adopts ultra-lean design. Source: Nokia Networks, via Ghosh 2018, slide 6.

    We identify the following:

    • Flexibility: OFDM sub-carrier spacing and symbol duration are flexible such that services with different requirements of bandwidth and latency can coexist. The design allows for wide range of deployments from outdoor macrocells to indoor picocells. Wide spectrum from sub-GHz to mmWave bands are supported. Symbol allocation within a slot is flexible.
    • Forward Compatibility: Design is such that it's easy to introduce new use cases in future. This is enabled by self-contained slots and beams, that is, they can be decoded without dependency on other slots or beams. This also relates to design flexibility: details are configured at runtime rather than fixed in specifications.
    • Ultra-Lean Design: LTE transmits regular reference signals, synchronization signals and system broadcasts. 5G is designed to minimize such "always on" transmissions. This improves network energy efficiency and reduces interference in high traffic load conditions. This also assists forward compatibility. Another related approach is device-centric mobility. A mobile sends out periodic reference signals that a base station measures, rather than monitor reference signals from many nearby cells.
  • What's the architecture of 5G NR?
    Overall architecture of 5G NG-RAN. Source: ETSI 2020a, fig. 4.1-1.
    Overall architecture of 5G NG-RAN. Source: ETSI 2020a, fig. 4.1-1.

    Next Generation Radio Access Network (NG-RAN) consists of gNB and ng-eNB. gNB serves a 5G UE over 5G New Radio (NR), a new air interface developed for 5G. gNB connects to 5G Core, though some can connect to 4G EPC as well. ng-eNB connects to 5G Core but serves a 5G UE over E-UTRA radio.

    gNB and ng-eNB are interconnected via Xn interface. In the user plane, Xn uses GTP-U over UDP/IP. In the control plane, Xn uses XnAP over SCTP. Thus, signalling packets have guaranteed delivery whereas user plane packets don't. Xn-U does data forwarding and flow control. Xn-C facilitates UE mobility management and dual connectivity.

    5G NR nodes connect to 5G Core via NG interface. Like Xn, NG-U uses GTP-U over UDP/IP, and NG-C uses NG-AP over SCTP. More specifically, NG-U connects to User Plane Function (UPF) and NG-C connects to Access and Mobility Management Function (AMF) in the core. NG-C and NG-U are also called N2 and N3 interfaces respectively.

  • What's the 5G NR protocol stack?
    5G NR protocol stacks. Source: ETSI 2020a, sec. 4.4.
    5G NR protocol stacks. Source: ETSI 2020a, sec. 4.4.

    The air interface between the UE and gNB is usually described in two planes:

    • User Plane (UP): Carries user data. Consists of PHY, MAC, RLC, PDCP and SDAP. SDAP is new in 5G (doesn't exist in LTE).
    • Control Plane (CP): Carries signalling such as sending system broadcasts, paging UEs, establishing connection, handover, measurement reporting, NAS messaging, etc. Consists of PHY, MAC, RLC, PDCP and RRC. In addition, the UE has Non-Access Stratum (NAS) layer that terminates on the network side in the 5G Core.

    PHY is commonly called Layer 1. MAC/RLC/PDCP/SDAP are called sub-layers of Layer 2.

    When transmitting, SDAP maps QoS flows to data radio bearers. PDCP maps (data or signalling) radio bearers to RLC channels. RLC maps RLC channels to logical channels. MAC does the scheduling and maps logical channels to transport channels. PHY maps transport channels to physical channels. When receiving, the layers map in the opposite direction.

  • What are the key principles or features of NG-RAN?
    NG-RAN features (left) and 5GC features (right). Source: ETSI 2020a, fig. 4.2-1.
    NG-RAN features (left) and 5GC features (right). Source: ETSI 2020a, fig. 4.2-1.

    An essential principle of NG-RAN is the logical separation of signalling and data transport networks. NG-RAN and 5GC functions are separated from transport functions, even if they happen to reside in the same equipment. Mobility of an RRC connection is fully controlled by NG-RAN.

    NG-RAN nodes can be further disaggregated into Radio Unit (RU), Distributed Unit (DU) and Centralized Unit (CU). By locating these parts at cell site or at cloud edge different deployment options are possible. Operators can decide based on the use case, CAPEX and OPEX. 3GPP has standardized the F1 interface between gNB-DU and gNB-CU, the W1 interface between ng-eNB-DU and ng-eNB-CU, and the E1 interface between gNB-CU-CP and gNB-CU-UP. Other industry bodies might standardize the RU-DU interface.

    NG-RAN has many functions: Radio Resource Management (RRM); routing of packets to AMF or UPF; encryption and integrity protection of data; IP and Ethernet header compression; connection setup and release; scheduling and transmission of system broadcasts and paging; QoS flow management; radio access network sharing; dual connectivity; support of network slicing; and more.

  • What role does each protocol layer play in NG-RAN?
    Downlink user plane L2 structure. Source: ETSI 2020a, fig. 6.7-1.
    Downlink user plane L2 structure. Source: ETSI 2020a, fig. 6.7-1.

    SDAP maps a QoS flow to a data radio bearer. It's not relevant to the control plane.

    PDCP does header compression/decompression using ROHC or EHC protocols. It encrypts/decrypts packets. It adds/checks integrity of packets. It supports both in-order and out-of-order delivery. It discards duplicates.

    RLC supports three transmission modes: Transparent Mode (TM), Unacknowledged Mode (UM), and Acknowledged Mode (AM). An RLC entity's functions are based on its mode. In AM, there's error correction through ARQ, duplicate detection and error detection. In AM and UM, SDUs can be segmented and there's sequence numbering; plus, SDUs can be discarded.

    MAC maps SDUs from one or more logical channels to transport channels. It does padding. It does error correction through HARQ, one per Component Carrier (CC). It prioritizes transmission towards UEs (downlink only), across logical channels of a UE, and UE resources.

    Among the PHY procedures are link adaption, power control, cell search, random access, and HARQ. PHY processing includes code block segmentation and CRC attachment, LDPC coding, rate matching, scrambling, modulation, layer mapping, and mapping to assigned resources and antenna ports.

  • How do 5G NR L2 sub-layers differ from LTE's E-UTRA sub-layers?

    SDAP is new in 5G NR. 5G Core can configure different QoS requirements for different IP flow of a PDU session. SDAP maps IP flows to data radio bearers that can provide the necessary QoS.

    PDCP does packet duplication when sending, and reordering and duplicate detection when receiving. This is done to satisfy URLLC use case. PDCP also includes integrity protection for user plane data.

    Unlike LTE, RLC doesn't concatenate RLC SDUs since something similar is done at MAC. Likewise, 5G RLC doesn't do reordering since the reordering done at PDCP is deemed adequate.

    MAC carries signalling for beam management done at PHY.

    Whereas LTE RRC has only two states (Idle and Connected), 5G RRC includes Inactive as an additional state. This enables devices to save power and quickly reconnect with minimal signalling. UE can also request specific system information instead of NG-RAN periodically sending the same.

  • What are the enhancements to 5G NR in Release 16?
    A summary of 5G NR enhancements in Release 16. Source: Qualcomm 2020, slide 8.
    A summary of 5G NR enhancements in Release 16. Source: Qualcomm 2020, slide 8.

    We summarize the main enhancements:

    • MIMO: MU-MIMO support of higher rank, multiple transmission and reception points (multi-TRP), better multi-beam management (useful in mmWave band), and extended uplink coverage (full power UL transmission).
    • URLLC: Using Coordinated Multi-Point (CoMP) reliability is improved. CoMP uses multi-TRP. Improved HARQ, flexible scheduling, inter-device service multiplexing and intra-device channel prioritization are other changes.
    • Time-Sensitive Networking (TSN): For industrial automation, TSN provides time-deterministic delivery of data packets.
    • Power Save: Wakeup Signal (WUS) lets a device skip the next low-power DRX (discontinuous reception) monitoring period.
    • Integrated Access and Backhaul (IAB): IAB allows a base station to provide wireless backhaul to neighbouring base stations.
    • NR-U: 5G can operate in unlicensed spectrum, either with a licensed/shared spectrum as anchor or in standalone mode.
    • Non-Public Network (NPN): For industrial IoT, private networks with small cells, dedicated resources and low latency are possible.
    • Cellular-Vehicle-to-Everything (C-V2X): NR-based sidelink is introduced. Multicast groups are defined based on distance and applications.
    • Positioning: Meets the accuracy requirements of 3 meters (indoor) and 10 meters (outdoor).



First drafts of two high-level documents TS 38.300: NR and NG-RAN Overall description; Stage-2 and TS 38.401: NR-RAN; Architecture description are published.


3GPP approves the first specifications for 5G, called "early drop" of Release 15. Specifically, it ratifies Non-Standalone (NSA) 5G New Radio (NR) specification. This enables vendors to start implementing the first 5G products. NSA 5G will allow operators to leverage existing 4G infrastructure. However, it can't support some use cases that require ultra-low latency and higher capacity.


Also part of Release 15, and called "main drop", 3GPP approves many specifications for 5G including the Standalone (SA) option. This allows operators without 4G networks to offer 5G service.


3GPP approves "late drop" of Release 15. This might aid in migrating from 4G to 5G, or NSA 5G to SA 5G. However, some vendors and operators don't see this as essential since Release 16 or 17 specifications could offer alternatives.


3GPP finalizes Release 16 specifications. This adds support for unlicensed spectrum. It improves on latency, power consumption, positioning and cellular-to-vehicle connectivity. Existing features enhanced by Release 16 include MIMO, beamforming, Dynamic Spectrum Sharing (DSS), Dual Connectivity (DC) and Carrier Aggregation (CA).


  1. Alleven, Monica. 2017. "3GPP declares first 5G NR spec complete." FierceWireless. December 20. Accessed 2018-02-20.
  2. Bertenyi, Balazs, Richard Burbidge, Gino Masini, Sasha Sirotkin, and Yin Gao. 2018. "NG Radio Access Network (NG-RAN)." Journal of ICT Standardization, vol. 6, no. 1 & 2, pp. 59-76, May. Accessed 2021-01-19.
  3. Bhushan, Naga, Tingfang Ji, Ozge Koymen, John Smee, Joseph Soriaga, Sundar Subramanian, and Yongbin Wei. 2017. "5G Air Interface System Design Principles." IEEE Wireless Comms, October. Accessed 2021-04-04.
  4. Brown, Gabriel. 2018. "New Transport Network Architectures for 5G RAN." Heavy Reading Reports, Fujitsu, October. Accessed 2021-01-19.
  5. Casaccia, Lorenzo. 2020. "Propelling 5G forward: A closer look at 3GPP Release 16." OnQ Blog, Qualcomm, July 7. Accessed 2021-01-19.
  6. Dano, Mike. 2019. "Another set of 5G standards was just released, but no one really cares." LightReading, April 5. Accessed 2020-12-22.
  7. Dryjanski, Marcin. 2018. "LTE and 5G Differences: Function Decomposition Between RAN and CN." Grandmetric, May 21. Accessed 2021-01-19.
  8. Ekström, Hannes. 2019. "Non-standalone and Standalone: two standards-based paths to 5G." Blog, Ericsson, July 11. Accessed 2020-12-22.
  9. ETSI. 2020a. "TS 138 300: 5G; NR; NR and NG-RAN Overall description; Stage-2." V16.3.0, November. Accessed 2021-01-19.
  10. ETSI. 2020b. "TS 138 401: 5G; NR-RAN; Architecture description." V16.3.0, November. Accessed 2021-01-19.
  11. EventHelix. 2018. "Ultra-Reliable Low-Latency Communication (URLLC)." Medium, May 29. Accessed 2021-01-19.
  12. Farkas, János, Balázs Varga, György Miklós, and Joachim Sachs. 2019. "5G TSN - integrating for industrial automation." Ericsson Technology Review, Ericsson, August 27. Accessed 2021-01-16.
  13. Fletcher, Bevin. 2020. "3GPP completes latest 5G NR spec with Release 16." Fierce Wireless, July 6. Accessed 2020-12-22.
  14. Ghosh, Amitabha. 2018. "5G New Radio (NR) : Physical Layer Overview and Performance." Presentation from Nokia Networks, IEEE Communication Theory Workshop, May 15. Accessed 2021-04-05.
  15. Goss, Michaela. 2020. "An overview of 3GPP 5G releases and what each one means." TechTarget, October. Accessed 2020-12-22.
  16. Parallel Wireless. 2019. "5G NR Logical Architecture and its Functional Splits." Parallel Wireless, September. Accessed 2021-01-19.
  17. Peisa, Janne, Patrik Persson, Stefan Parkvall, Erik Dahlman, Asbjørn Grøvlen, Christian Hoymann, and Dirk Gerstenberger. 2020. "5G evolution: 3GPP releases 16 & 17 overview." Ericsson Technology Review, Ericsson, March 9. Accessed 2021-01-19.
  18. Qualcomm. 2020. "Propelling 5G forward: Key 3GPP Release 16 inventions." Qualcomm, June. Accessed 2021-01-15.
  19. Razani, Hooman. 2018. "Getting your G's and N's Right." Award Solutions, November 30. Accessed 2021-01-19.
  20. Zaidi, Ali. 2017. "Three design principles of 5G New Radio." Blog, Ericsson, August 8. Accessed 2021-04-05.
  21. Zaidi, Ali A., Robert Baldemair, Mattias Andersson, Sebastian Faxér, Vicent Molés-Cases, and Zhao Wang. 2017. "Designing for the future: the 5G NR physical layer." Ericsson Technology Review, Ericsson, July 24. Accessed 2021-01-15.

Further Reading

  1. ETSI. 2020a. "TS 138 300: 5G; NR; NR and NG-RAN Overall description; Stage-2." V16.3.0, November. Accessed 2021-01-19.
  2. ETSI. 2020b. "TS 138 401: 5G; NR-RAN; Architecture description." V16.3.0, November. Accessed 2021-01-19.
  3. Casaccia, Lorenzo. 2020. "Propelling 5G forward: A closer look at 3GPP Release 16." OnQ Blog, Qualcomm, July 7. Accessed 2021-01-19.
  4. Intel. 2018. "5G NR - Driving Wireless Evolution into New Vertical Domains." Intel, August. Accessed 2021-01-15.

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Devopedia. 2021. "5G New Radio." Version 5, April 5. Accessed 2021-04-05. https://devopedia.org/5g-new-radio
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Last updated on
2021-04-05 06:25:17