LitePoint’s Khushboo Kalyani has developed this two-part blog series on 5G sub-6GHz and mmWave test considerations. Throughout this series of blog posts, you’ll learn about the promise of 5G and some of the physical layer changes that drove crucial RF hardware and antenna changes and important test challenges and considerations.

5G Physical Layer Changes Support Diverse Application Use Cases

5G is making its debut and it is expected to impact many industry sectors in a big way. According to the Global mobile Suppliers Association (GSA) November 2020 device ecosystem report, nearly 500 5G devices have been announced. Another report from September 2019 in DIGITIMES projects that by 2024, out of the nearly 1.6 billion devices, approximately 45 percent are expected to be 5G mobile devices. This would represent a huge amount of growth over the next few years.

Unlike previous generations of wireless technologies that typically focused on supporting cellular communication or mobile telephony, 5G promises to offer connectivity and support for a diverse range of devices spanning multiple different industry verticals. As per GSA’s November 2020 device ecosystem report, besides phones, almost 19 different 5G device form factors have been announced, which include hotspots, customer premises equipment (CPE), snap-on dongles, laptops, in-vehicle routers, drones, robots and many other devices.

5G Physical Layer Changes

In order to support a wide variety of devices, as well as a number of exciting new application use cases, a number of physical layer changes were brought in to 5G.

One of the most pronounced differences is seen in terms of the spectrum. With LTE bound to operate in the sub-3GHz frequency range, regulatory bodies around the world have opened up a wide range of spectrum for 5G use. There are two different frequency band classifications for 5G. Frequency range 1 (FR1), spans from 410 MHz – 7.125 GHz. Frequency range 2 (FR2), also known as millimeter wave (mmWave), supports operation in the 24.25 GHz – 52.6 GHz range.

The primary reason for adding new spectrum was its support for large channel capacity and bandwidth. Unlike LTE, which supported a maximum bandwidth of 20 MHz, 5G offers bandwidth as high as 100 MHz in FR1 and up to 400 MHz in FR2. Such high bandwidths can translate into data rates as high as 10Gbps.

Another key facet of 5G which facilitates its implementation and operation in varied application use cases is the support for flexible subcarrier spacing (SCS). In addition to the 15KHz fixed subcarrier spacing rendered by LTE, 5G offers additional numerologies of 30, 60, 120 and 240KHz. There are two major advantages of this.

First, the higher the carrier spacing, the smaller the slot size, which allows for an optimum allocation of resources based on the use case. For example, an enhanced mobile broadband (eMBB application) with extremely high data rate would require wider slot durations (smaller SCS) to accommodate large data payloads. Whereas an IoT device with significantly lower payload, may require smaller slot duration.

The second benefit of flexible numerology is the resistance to doppler shift using wide carrier spacing. Not only does this mitigate interference but improves reliability at mmWave frequencies. Which is why smaller sub carrier spacings – 15 KHz and 30 KHz are not supported for operation in FR2.

One of the most crucial features to aid operation in the mmWave frequency range is the support for beamforming. While MIMO was supported in LTE, in the form of spatial multiplexing, at mmWave frequencies higher path losses make it difficult to maintain adequate SNR. Hence it becomes paramount to compensate for the loss by steering radio energy in the desired direction. Beamforming makes use of multiple antenna arrays to increase SNR and chances of signal reception.

Application Use Cases

What are the applications that are enabled by these physical layer changes? 5G is designed to service three broad categories of use cases – eMBB, ultra-reliable low-latency (URLLC) and massive machine-type communication (mMTC), each with disparate requirements for performance. Into 2021, 5G will continue to be focused on eMBB and fixed wireless access. Between 2021-2023, 5G will evolve to support URLLC private networks and mMTC.

These 5G application use cases require high data rates, minimum latency and more optimized communication. For example, certain applications like augmented/virtual reality and video streaming are data hungry and need wider bandwidth and higher throughput. Other use cases like industrial and vehicle automation are intolerant of latency, demand reliability in the order of 10^-9 and latency within one millisecond. A third category of use cases, arising from the widespread need for connectivity among IoT and smart devices, calls for a technology that is able to support dense communication.

Operators around the world are trying to find the best frequency band to support these use cases. For instance, lower frequency bands offer limited capacity but are being used to extend the coverage across the country. Mid band frequencies offer the most optimum coverage and capacity and are being widely deployed around the world. Higher frequency bands in mmWave ranges are primarily used to serve data hungry / capacity hungry applications like AR/VR or video streaming.

Evolution of 5G in Support of Use Cases

3GPP Release 15 focused more on providing a platform for enhanced mobile broadband use cases. This included data-hungry applications that require higher bandwidth, as well as fixed wireless access communication.

Release 16 was finalized in June 2020 and included enhancements for supporting URLLC use cases or industrial internet of things (IIoT) applications. This includes private networks that are needed by industrial facilities and factories for factory automation or infrastructure monitoring. Some enhancements were made in Release 16 in terms of multiple transmission interception to improve link reliability and latency, which are features needed for better C-V2X or autonomous communication. The release also included support for better positioning applications, support for deployment of 5G in unlicensed bands and better power saving features – all geared toward supporting IIoT applications.

The next 5G specification, Release 17, will come in 2022 and will focus on continued expansion of the 5G specification with enhancements focused on mMTC and NR-Light devices such as wearables or industrial sensors.

With these use cases in mind and the physical layer changes brought into 5G to support these use cases, my next blog post will explore some test challenges and considerations for 5G. In the meantime, please visit the replay of my webinar on this topic.