What is 5G New Radio (NR)?

Birth of 5G NR with Release 15 release in December 2017, followed by June 2018
Figure 1: 5G Standardization Timeline

4G LTE is a capable technology that has brought improvements and innovations catering to the widespread use of smartphones. The work on LTE started more than ten years ago as illustrated in Figure 1. Since then, it evolves over the years with new specifications as seen in LTE advanced phase A, B and C.

In particular, LTE advanced phase C is currently going on and will be complete in a couple of years. Furthermore, this LTE technology is going to be available along with the latest 5G specification, i.e., 5G New Radio (5G NR).

5G NR Timeline: Studies to Release-15

3GPP wanted to address new requirements and leverage new technologies which weren’t part of LTE development. Hence, the development of new radio access tech that is 5G NR got underway. The 5G NR first version came to existence in December 2017 and reused many of the features of LTE.

Also, the first NR version highlights the non-standalone operation where devices depend on LTE for the initial access and mobility. Initial access is a method for a device or user equipment (UE) to find its intended cell and then receive appropriate system information followed by requesting a connection via random access.

As shown in Figure 2, with Release-15 final version in June 2018, the 5G specification also indicates support for standalone NR operation. In standalone mode, a 5G base station connects directly to its core network while managing user and control plane functions. There are few more details about these operational modes which we discuss in a later section.

Timeline of 5G NR development within 3GPP
Figure 2: Timeline of 5G New Radio (NR) development within 3GPP

Key features of 5G NR over LTE

The 5G NR excels in providing many key features in comparison to 4G LTE. Few of them are as follows,

  • Exploitation of much higher-frequency bands for the purpose to obtain additional spectra
    – To support very wide transmission bandwidths and the associated high data rates
  • Ultra-lean design to improve network energy performance and minimise interference
  • Forward compatibility to prepare for future
    To accomplish this, NR presents a radio-interface design that allows for substantial future evolution with new technologies. Also, enabling new services with yet unknown characteristics and requirements. However, at the same time support legacy devices on the same mobile operator. According to the 3GPP technical specification group (TSG) document [1], the following design principles guide NR forward compatibility,
  1. Maximise the amount of time and frequency resources that can be flexibly utilised or that can be left blank without causing backward compatibility issues in the future
  2. Minimising transmission of always-on signals
  3. Confining signals and channels for physical layer functions within a configurable or allocable time or frequency resource
  • Beam design with beamforming: First, a brief note on Beamforming. Beamforming uses multiple antennas to control the direction of a wavefront. It does so by appropriately weighting the magnitude and phase of individual antenna signals in an array of several antennas. For instance, if the same signal transmits from multiple antennas with sufficient spacing or distance between them.

Then, for a receiver at any location, is going to receive multiple copies of the same signal. Now, note that depending on the location of the receiver, the signals may be in opposite phases and if so averages each other out. The other option is that they effectively add up if the different copies are in the same phase or anything in between.

Beamforming in NR with multiple antennas at TX and RX
Example scenario of Beamforming in 5G NR (source [2])

NR supports a large number of directed antenna elements for both transmission and reception. At higher-frequency bands, the purpose of a large number of antenna elements is to provide beamforming for spreading out coverage. Also, at high frequencies, analog beamforming employs where the beam orients after digital to analog conversion.

On the other hand, at low-frequency bands, those high number of antenna elements drive massive MIMO. Also, at lower-frequency bands, the possibility to separate users spatially increases both in uplink and downlink but requires that the transmitter has channel knowledge.

5G NR Use-cases

Broad classification of 5G NR use-cases
Figure 3: High-level overview of 5G NR Use-cases classification

eMBB (Enhanced mobile broadband)

eMBB corresponds to a straightforward evolution of the mobile broadband services of today. It enables even more extensive data volumes and further enhanced user experience. For example, by supporting even higher end-user data rates, high capacity and high user density as in wireless hotspots.

The second use case of eMBB covers wide-area coverage that requires mobility and seamless user experience while having lower requirements on data rates and user density.

mMTC (massive machine-type communication)

mMTC corresponds to services that characterise a massive number of devices. For example, remote sensors, actuators, and monitoring of various industrial equipment. The critical requirements for such services include little device cost and low device energy consumption. In particular, the longevity of device battery life should last at least several years.

Also to note that each device consumes and generates only a relatively small amount of data. Hence, support for high data rates is of less importance.

URLLC (Ultra-reliable and low-latency communication)

URLLC services intend to cover human and machine centric communication. These services require very low latency, extremely high reliability, and high availability. Examples include Vehicle-to-Vehicle communication involving traffic safety and remote medical surgery. Few other examples include wireless automatic control of industrial equipment and factory automation.

On the human-centric front, use-cases are 3D gaming and next-generation Internet. The next-gen Internet has the characteristics of low latency, high availability, a very high benchmark for data rates, reliability, and security.

The above classification of 5G NR into three distinctive classes by 3GPP is to simplify the definition of requirements. As 5G services get mature, there will be many use cases that don’t conform precisely into these broad classes.

For instance, there might be a service that requires no such stringent latency requirements, but high reliability is a must. Also, there can be use-cases requiring low-cost devices whose battery life longevity won’t be critical.

5G NR Radio-Interface Architecture

The 5G NR Radio-access network, LTE core network known as Evolved Packet Core (EPC), and 5G Core network form the core components of the radio-interface architecture. We also discuss deployment modes of 5G NR in this section.

Enhanced Packet Core (EPC)

EPC is a multi-access core network based on the Internet Protocol (IP) that enables mobile operators to deploy and operate one common packet core network for 3GPP radio access (4G LTE, 3G, and 2G). It is also applicable to non-3GPP radio access (WLAN, WiMAX), and fixed access (Ethernet, DSL, cable, and fiber).

The EPC set-up is around three fundamental paradigms of mobility, policy management, and security. EPC also characterises the data and control planes.

5G Core Network (5GCN)

The motivation behind 5G core network is EPC and it builds upon the latter with three new areas of enhancement, namely, service-based architecture, support for network slicing, and control-plane/user-plane split. A service-based architecture is a basis for the 5G core, which means that the specification focuses on the services and functionalities provided by the core network, rather than nodes as such.

The core network as of today is already often highly virtualised with the core network functionality running on generic computer hardware. A network slice is a logical network serving a particular business or customer need. It consists of the necessary functions from the service-based architecture all coming together nicely.

For example, one network slice is set to support mobile broadband applications with full mobility support, similar to LTE. Another slice can be set up to help a specific fixed, latency-critical industry-automation application solution.

These network slices will run on the same physical core underlay and radio networks. However, from the end-user application perspective, they appear as independent networks. In many aspects, it is analogous to configuring multiple virtual machines on the same physical computer.

Concerning control plane and user-plane split, including independent scaling of the capacity of the two. For example, if there is a need for more control plane capacity, it should be straightforward to add it without affecting the user-plane of the network. The new 5G core network set-up is in parallel to the NR radio access and is capable of handling both NR and LTE radio accesses.

Radio Access Network

The radio access network has two types of nodes connected to the 5G core network that is eNB and gNB. When eNBs nodes are for LTE radio access and gNBs for NR radio access then such a radio access network is called as NG-RAN or RAN.

eNB:

It stands for E-UTRAN Node B, also known as Evolved Node B. E-UTRA (Evolved Universal Terrestrial Radio Access) is the air interface of 3GPP Long Term Evolution (LTE) upgrade path for mobile networks. An eNB node serves LTE devices using the LTE user-plane and control-plane protocols. It acts as the base station for LTE.

gNB:

It stands for next-generation Node B. Also, gNB is a logical node and doesn’t translate into a physical implementation. An example implementation scenario of a gNB is a three-sector (sector antennas) site, where a base station handles transmissions in three cells, with each cell having its own set of frequency channel(s). A gNB node serves NR devices using the NR user-plane and control-plane protocols. It acts as the base station for 5G NR.

Deployment modes of 5G NR - Non-standalone and stand alone mode
Figure 4: Deployment modes of 5G NR

5G NR deployment mode: Non-standalone

In this mode, the EPC core network connects to the eNB (LTE) as shown in Figure 4 (a) above. LTE handles all control-plane functions and use of NR is only for the user-plane data. The gNB (NR) connects to the eNB (LTE) and user-plane data from the EPC forwards from the eNB to the gNB.

A couple of variants also exist which are as follows. First, the user-plane parts of both the eNB and gNB directly connect to the EPC. Second, only the gNB user plane connects to EPC, and user-plane data to the eNB gets a route via the gNB.

5G NR deployment mode: Stand-alone

In this mode, the gNB (NR) connects directly to the 5G core network. gNB (NR) handles both user-plane and control-plane functions as shown in Figure 4(b). Furthermore, 5G NR in this mode leverages SDN (software-defined networking) to create optimal network slices and deliver on 5G’s promise.

In Figure 5 below, it shows how 5G NR stand-alone mode can co-exist with the non-standalone mode to deliver on 5G’s potential.

NSA as a stepping stone to SA deployment mode in 5G NR
Figure 5: NSA as a precursor to SA operation for highly capable 5G services

5G NR Inter-working with LTE

Very Tight Inter-working between LTE and 5G NR
Figure 6: Tight inter-working between LTE and 5G NR

The rationale behind inter-working between 5G NR and LTE is as follows. We know that full coverage is difficult to achieve at higher frequencies. Therefore it necessitates inter-working with systems running at lower frequencies.

For instance, the coverage imbalance between uplink and downlink plays out when they are present in different frequency bands. Another dimension is the difference in transmit power for the uplink and downlink scenario.

Due to high transmit power for the base station in comparison to the mobile device, this results in the downlink data rates to be bandwidth-limited. To counter this, it is more suitable to operate the downlink in a higher frequency band so as to leverage wider available bandwidth.

On the other hand, the uplink usually is power-limited and thus reduces the necessity for the wider bandwidth. It is also true that higher data rates could be achieved even on lower-frequency spectra even with less available bandwidth due to the effect of lower radio-channel attenuation.

By employing inter-working, a high-frequency NR system complements a low-frequency system. The lower-frequency system can be either be 5G NR or 4G LTE, and NR supports inter-working with either of these. But it is seen often that the lower frequency bands are primarily held by LTE.

Coming to LTE-NR spectrum coexistence, it depicts that a mobile operator deploys NR in the same spectrum as an already existing LTE deployment. This carves a path for charting out early NR development in lower-frequency spectra while making sure that amount of spectrum available to LTE hasn’t been reduced.

For instance, when NR deploys in the same spectrum as LTE in such a way that the overall spectrum capacity can be shared dynamically between them. Furthermore, NR allows for dual-connectivity with LTE, meaning devices may have simultaneous connectivity to both LTE and NR. We will explain LTE-NR dual-connectivity in further detail below.

LTE-NR Dual Connectivity

Consider a device or UE (User Equipment) having simultaneous connectivity to a small-cell layer for NR in high-frequency bands and a macro layer based on LTE as an overlay in the low-frequency band. This scenario represents an appropriate scenario of LTE-NR dual connectivity.

The LTE macro layer would then provide the master nodes to ensure that the control plane is active even if the connectivity to the high-frequency small-cell layer see a loss temporarily.

In this case, the NR layer provides very high capacity and very high data rates, while dual-connectivity to the lower-frequency LTE-based macro layer offers additional robustness to the less durable high-frequency small-cell layer.

LTE-NR dual connectivity scenario
Figure 7: LTE-NR dual-connectivity scenario (source [2])

5G NR-LTE Co-existence scenarios:

Scenario depicting 5G NR and LTE co-existence: uplink/downlink
Figure 8: Example scenarios of 5G NR and LTE co-existence (source [2])

Figure 8 illustrates the NR and LTE co-existence. In the first scenario, shown in the left part of the figure, there is LTE-NR coexistence in both downlink and uplink.

However, in the second scenario, as seen in the right part of the figure, co-existence can be seen only in the uplink transmission direction. Typically, within the uplink part of a lower-frequency paired spectrum, with NR downlink transmission taking place in the high-frequency range dedicated to NR. For this scenario, 5G NR supports a supplementary uplink.

Summary

In this article, we gave an overview of 5G New Radio (NR) which is the latest 5G standard for mobile and wireless systems. We cover the timeline of 5G NR releases by 3GPP and fundamental deployment mode: non-standalone and standalone mode. We then discuss a few critical features of 5G NR over LTE, namely, ultra-lean design, forward capability, beamforming with a beam-centric design.

Moving on, we present 5G NR use-cases proposed by 3GPP and then go further to discuss 5G radio-interface architecture. In particular, we cover its core components and deployment modes. Finally, we navigate our write-up to explain 5G NR inter-working with LTE and how inter-working leads to LTE-5G NR dual connectivity and co-existence scenarios.

In our subsequent articles, we are going to cover more specific topics for 5G NR such as Spectrum flexibility (carrier aggregation), frequency bands for NR, new waveforms and Initial Access.

References

  1. 3GPP R1‑163961: Final Report of 3GPP TSG RAN1 #84bis v1.0.0 by ETSI
  2. 5G NR: The Next Generation Wireless Access Technology (Book) by Erik Dahlman, Stefan Parkvall, Johan Skold