Demystifying 5G to understand its complexity
Of course, the early steps on this journey are somewhat tentative. The 5G-infrastructure deployments this year will be Non-Standalone (NSA); using 5G frequencies for high-speed data exchanges while relying on 4G technologies to manage connections to infrastructure and servers. So far, the test specifications for 5G devices are not fully finalised. For NSA, although the 3GPP TS38.521-3 transmitter and receiver tests for interworking with LTE in Frequency Range 1 (FR1) below 6 GHz and in the FR2 mm-wave bands (24 GHz-52 GHz) are quite well developed, others such as performance tests (38.521-4) and radio resource management (RRM) test requirements have been standardized, yet there are still open points to be clarified.
Happily, the corresponding specifications for standalone (SA) operation, namely TS38.521-1 for FR1 and TS38.521-2 for FR2 are more advanced, although other parts of the SA standards will not be approved until later this year.
Anyone currently developing products or services to use 5G networks must work with the fact that test specifications are not complete, which could lead to compatibility or performance problems. They need to know how to handle this, while standards makers work quickly to remedy the situation.
There are technical challenges associated with testing 5G subscriber devices, too. The active antenna systems needed to ensure efficient beamforming for operation at mm-wave frequencies require highly integrated PCBs comprising antennas, amplifiers and analog phase shifters to keep internal attenuation low and circuit dimensions small. RF connectors for traditional conducted measurements are not available, so testing has to be done Over the Air (OTA). With OTA the distance between the DUT and the antenna of the measurement system needs to be considered. This distance is linked to the so called Fraunhofer distance describing the boundary between near field and far field. In far field the wave propagation can be described as plane wave and all measurements like modulation quality, transmit power and receiver sensitivity can be performed. The far field distance depends on the wavelength and the dimensions of the antenna aperture under test. At higher frequencies, the resulting larger distance would make far field analysis more difficult, particularly for FR1 tests that would require a very large test chamber, maybe 10 metres or more in length. New test techniques, and equipment such as Compact Antenna Test Range (CATR) solutions that are suitable for laboratory use, are emerging to overcome these challenges.
Another concern that arises during product testing is assessing the temperature sensitivity of the amplifiers and phase shifters used for beam forming and steering in the complex antenna array systems of 5G NR mm-Wave radios. Rapidly heating or cooling a large test chamber is impractical, so Rohde & Schwarz has developed a solution for isolating the environment around the DUT allowing the temperature to be varied without affecting the radiation parameters.
Test practices are also set to change significantly with the change to OTA testing. For example, tests must be performed in three dimensions to check for proper beam-forming operation, so a suitable 3D positioner must be used and the position of the unit under test recorded accurately in each case.
The future: more services, more markets, more complexity
The current Release 15 of the specification standardises the fundamental features needed for network operators to provide 5G enhanced mobile broadband (eMBB) services. Ultimately, 5G will support massive Machine-Type Communications (mMTC) and Ultra-Reliable Low-Latency Communication (URLLC) with the change to SA deployments, making many new and diverse types of services possible. These are expected to include advanced automation and cloud robotics for Industry 4.0, e-health applications, autonomous driving, and many others that are not yet conceived. With their arrival, the scope of test activities will extend to include safety and security aspects such as reliability, deterministic low latency, authentication, and encryption.
Already industry bodies are forming, such as the 5G Automotive Association (5GAA) and the 5G Alliance for Connected Industry and Automation (5GACIA), comprising chip makers, industry-specific corporations, and telecom operators interested in developing new ideas that will leverage 5G for the benefit of these specific industries.
With so many diverse interests, we can expect numerous new proposals to come forward that will mould and shape 5G infrastructures, devices, applications, and services. The sheer flexibility to fulfil multiple demands and support new applications will require all involved to open their minds more widely.
To provide this almost limitless flexibility, 5G is an extremely complex technology. Evidence of this complexity can be seen by looking at the 3GPP’s timeline for standardization. Release 15 started with an “early drop” in December 2017, necessary for the first deployments to go ahead, while more time has been needed to complete the planned “late drop” — now scheduled for June 2019 – that finalises further specifications. The task of defining work items for the next Release 16 has already started and is currently discussing new features and services such as C-V2X, 5G NR in unlicensed bands, and URLLC support.
In addition to the complexity, the great diversity of services 5G is expected to support – and their differing requirements in terms of bandwidth, data volume, response time – means ensuring adequate Quality of Service (QoS) for each is critical for network resources to be managed efficiently.
From the user perspective, an acceptable Quality of Experience (QoE) is sought. With large numbers of devices and a wide variety of services, leveraging networks’ mMTC and URLCC capabilities, defining and testing QoE, and determining suitable thresholds for each metric is set to become a much more complex and challenging task than in previous technology generations.
Join the community
Covering all of these all under one roof, so to speak, demands a complex network: the task of grasping this complexity, and understanding it, is no small challenge.
Rohde & Schwarz’s Demystifying 5G event brings people together from across the industry to learn from speakers with special expertise and to network with each other. Building on the model established by the successful Demystifying EMC days, Demystifying 5G is not a marketing seminar but a forum for sharing valuable information about standards, regulations, best practices, and technical tips.
The program will start with a high-level view of 5G, its current status globally, and the technology framework. Two in-depth presentations will look at the air interface, including beam forming and managing signals and channels, as well as requirements and test procedures for OTA equipment testing. There will also be test demonstrations, shorter sessions on protocol testing and network-performance measurements, and a formal opportunity for joint discussion and questions.
The scope and complexity of 5G mean gaining an understanding, to provide equipment and services to our target markets, is indeed a journey that begins with a single step. The same philosopher – Lao Tzu – also observed that we should do the difficult things while they are easy and do the great things while they are small. Although there is nothing small and easy about 5G, even now, tougher challenges lie ahead. There is no better time to start this journey.
Demystifying 5G will take place at The Royal Berkshire Conference Centre, Madejski Stadium, Reading on the 21 May 2019. More information and registration at https://www.rohde-schwarz.com/uk/seminars___trainings/uk-ireland-seminar-programme/demystifying-5g-seminar/demystifying-5g-seminar_250963.html
About the author:
Reiner Stuhlfauth is Technology Manager Wireless at Rohde & Schwarz International GmbH – www.rohde-schwarz.com