Three design principles of 5G New Radio
Robotic surgery, virtual-reality classrooms, self-driving cars, and broadband access everywhere. These are just the tip of the iceberg when it comes to what people expect to do with 5G wireless access. 5G New Radio (NR) is designed to be flexible, forward compatible and ultra-lean. Our view is that these design principles are dealmakers to support full range of future applications.
5G wireless access is being developed with three broad use case families in mind:
- Enhanced mobile broadband (eMBB)
- Massive machine-type communications (mMTC)
- Ultra-reliable low-latency communications (URLLC)
5G will encompass both an evolution of today’s 4G (LTE) networks and the addition of a new, globally standardized radio access technology known as New Radio (NR). NR will operate in the frequency range from below 1 GHz to 100 GHz with different deployments. Flexibility, ultra-lean design and forward compatibility are key principles on which NR is being built, as illustrated below:
Flexibility, forward compatibility, and ultra-lean design are fundamental design principles of NR
Let’s look at what these principles mean and how NR physical layer components (modulation schemes, waveform, frame structure, reference signals, multi-antenna transmission and channel coding) follow them.
Flexible design is necessary for addressing wide range of carrier frequencies (sub 1 GHz to 100 GHz), different deployment types (macro, micro, pico cells), and diverse use cases (eMBB, mMTC, URLLC) with extreme and sometimes contradictory requirements.
Physical layer components of NR are flexible and scalable. For example, there exist wide range of QAM based modulation schemes, OFDM waveform with scalable numerology, LDPC codes with rate-compatible structure, and frame structure with flexible slot durations. Reference signals can be beamformed with configurable densities in time domain and frequency domain. Different antenna solutions and techniques can be employed under a flexible channel state information acquisition and reporting framework.
2. Forward compatibility
3GPP is taking a phased approach for NR standardization. First standardization phase with limited NR functionality will be completed by 2018, followed by a second standardization phase that fulfills all the requirements of IMT-2020 (the next generation of mobile communication systems to be specified by ITU-R) by 2019. It is likely that NR will continue to evolve beyond 2020, with a sequence of releases including additional features and functionalities. Since NR must support a wide range of use cases – many of which are not yet defined – forward compatibility is of utmost importance.
Forward compatibility in NR is achieved by self-contained and well-confined transmissions. Self-containment means that data in a slot and a beam is decodable without dependency on other slots and beams. Well-confined transmissions refer to keeping transmissions confined in frequency and time domains to allow future inclusion of new types of transmissions in parallel with legacy transmissions.
3. Ultra- lean design
Cellular networks transmit certain signals at regular intervals even when there is no data to transmit to any user. Reference signals, synchronization signals, and system broadcast information are examples of such transmissions. Ultra-design refers to minimizing these “always on” transmissions. Network should transmit signals only when necessary. Ultra-lean design significantly improves network energy efficiency, which is vital for sustainable society, reducing network operational expenses, and enabling network deployments without access to reliable power grids. Ultra-lean design reduces interference in high traffic load conditions. Ultra-lean design also enhances forward compatibility of NR because it is hard to modify “always on” transmissions without degrading performance of legacy devices.
NR has four main reference signals: demodulation reference signals, phase tracking reference signals, sounding reference signals, and channel state information reference signals. These signals are only transmitted when necessary, making NR design ultra-lean.
Further details about the NR physical layer can be found in this article for Ericsson Technology Review: Designing for the future: the 5G NR physical layer.