Making 5G NR a Commercial Reality – A Unified, More Capable 5G Air Interface

| Wanshi Chen

There is insatiable demand for mobile broadband. In December 2017, as part of 3GPP’s Release 15, a first version of 5G new radio (NR) was declared complete. The first version is a non-standalone (NSA) version where a 5G NR carrier leverages 4G LTE for coverage and mobility while enabling a fast introduction of 5G NR to enhance user plane performance and efficiency. The standalone version of 5G NR is expected to be ready by June 2018.

5G NR is essential for next generation mobile experiences, providing fiber-like data speeds, low latency for real-time interactivity, more consistent performance, and massive capacity for unlimited data. In addition, 5G expands the mobile ecosystem to new industries. It provides diverse services including traditional enhanced mobile broadband (eMBB), new verticals such as massive machine-type communications (mMTC), ultra-reliable low-latency communications (URLLC), and cellular vehicle-to-everything (C-V2X), and scalability to address a tremendous variety of requirements. It covers diverse spectra, including sub-6 GHz and millimeter wave (mmWave), in order to get the most out of a wide array of spectrum bands/types. It also supports various deployments, from macro to indoor hotspots, with support for a range of topologies.

The first version of 5G NR establishes the foundation for 5G NR eMBB and beyond and employs a set of key enabling techniques. These include:

  • A scalable Orthogonal Frequency-Division Multiplexing-based air interface, with subcarrier tone spacing ranging from 15 kHz to 240 kHz. It can efficiently address diverse spectra, deployments, and services while reducing FFT processing complexity for wider bandwidths with reusable hardware.
  • A flexible slot-based framework, necessary for low latency, URLLC, and forward compatibility. In particular, it introduces a self-contained slot structure with the ability to independently manage resources on a per-slot basis and avoid static timing relationships across slots. The duration of a slot is also salable (e.g., 1 ms, 0.5 ms, 0.25 ms, 0.125 ms) in order to accommodate diverse latency/QoS requirements. One example of a slot type is a time-division-duplex-like self-contained slot where a single slot may provide opportunities for downlink and uplink scheduling, data, HARQ response, and uplink sounding. Another example is a data-centric slot (e.g., a downlink or an uplink data-only slot). A slot may also contain a mini-slot optimized for shorter data transmissions (e.g., URLLC). It is also possible to have a blank slot, which is designed to facilitate future feature introductions.
  • Advanced channel coding. LDPC is used for 5G NR data channels, providing high efficiency with significant gains over 4G LTE Turbo encoding, particularly for large block sizes suitable for eMBB. It brings low complexity and enables an easily parallelizable decoder scaled to achieve high throughput. In addition, it offers low latency, where efficient encoding/decoding enables shorter transmission time at high throughput. For downlink and uplink control channels, Polar coding has been adopted, which gives reliable control channel transmissions.
  • Massive MIMO, a key enabler for utilizing higher spectrum bands such as 4 GHz with existing 4G LTE sites. 5G NR is optimized for TDD reciprocity procedures using uplink sound reference signals. It further enhances channel state information-reference signal (CSI-RS) design and reporting mechanisms compared with that of 4G LTE. It also employs advanced high-spatial resolution codebook supporting up to 256 antennas.
  • Mobilizing mmWave. mmWave is the new frontier of mobile broadband, with wide bandwidths (e.g., 400 MHz for a carrier) for extreme capacity and throughput. Beamforming and beam-tracking are essential for mobilizing mmWave. Innovations in 5G NR overcome challenges such as significant path loss in bands above 24 GHz, mmWave blockage from objects like hands, bodies, walls, and foliage, and fitting mmWave design in smartphone form factor and thermal constraints. 5G NR enables mmWave to be deployed with very dense network topology and spatial reuse (~150–200 m inter-site distance). 5G NR also supports the tight integration of mmWave with sub-6 GHz carrier frequencies.

For the next steps, many new additional features are expected to be further investigated and specified in 5G NR. 5G NR will provide more dedicated support for URLLC services (e.g., a reliability level of up to 10-5 block error rate (BLER) subject to a 1 ms delay budget). While LTE C-V2X supports both basic and some enhanced safety, 5G NR for C-V2X is expected to bring higher throughput, higher reliability, wideband ranging and positioning, and lower latency, which will eventually enable new capabilities for the connected vehicle, such as sensor sharing, intention/trajectory sharing, wideband ranging and positioning, local high definition, and maps/“bird’s eye view.” 5G NR is also studying the possibility of further enhancing the support of the massive Internet of Things via non-orthogonal multiple access (NOMA). In addition to the licensed spectrum, it is important to investigate 5G NR operation in both unlicensed and shared spectra, valuable for a wide range of deployments such as aggregation with licensed spectra, enhanced local broadband services, and private 5G networks. Integrated Access and Backhaul (IAB) is also being studied for cost-efficient dense deployments to improve coverage and capacity while limiting backhaul cost. There are also many other features under consideration, including enhanced broadcast, non-terrestrial networks, and flexible duplex.

Wanshi Chen is currently 3GPP TSG RAN1 – a work group responsible for physical layer over-the-air standardization — Chairman appointed in August 2013.

Wanshi Chen has over 17 years of experiences in telecommunications in leading telecom companies including operators, infrastructure vendors, anduser equipment vendors. From 2006, he has been with Qualcomm Corporate R&D contributing to system design, prototyping and implementation, and standardization of 4G LTE/LTE-Advanced and more recently 5G (New Radio or NR). He has been attending 3GPP TSG RAN1 for over 10 years, representing Qualcomm and playing an instrumental role in 4G and 5G standardization, as a Vice Chairman from August 2013 for 4 years, and as Chairman starting from August 2017. From 2000 to 2006, he worked at Ericsson, San Diego, responsible for 3GPP2 related system design, integration, and standardization. During 1996 and 1997, he worked as an engineer for China Mobile, primarily participated in wireless network maintenance and performance optimization.   Wanshi Chen is a recipient of Qualcomm’s IP Excellence Award, Upendra Patel Achievement Awards for Outstanding Contributions to LTE, and Super Qualstar Award from Qualcomm CR&D.   The highest degree that Wanshi Chen has received is a Ph.D. degree in electrical engineering from the University of Southern California, Los Angeles, CA, USA.   Wanshi is an avid runner. He ran the Boston Marathon in April 2017 with a time of 3 hours and 8 minutes.