5G, the next generation of mobile networks, promises to deliver faster and more reliable communication. It will bring a paradigm shift towards a user- and application-centric technology framework to support three key use cases: enhanced mobile broadband (eMBB) supporting the ever-increasing end-user data rate and system capacity; massive machine-type communications (mMTC) ensuring cost-efficient and robust connectivity among billions of devices without overloading the network; and ultra-reliable low latency communication (URLLC) that supports the new needs of vertical industries like autonomous driving, remote surgery for eHealth and cloud robotics for Industry 4.0.

These use-case families would require new technology equipment – from components and chipsets to assembled user devices and base stations. This poses challenges for product development. While network and end-user equipment developers have been making steady progress in addressing these challenges, the development of test and measurement (T&M) equipment that enables developers to evaluate the performance of the new equipment will be critical to successful 5G roll-out. T&M products would also be required to ensure standards compliance of this new equipment in the lab, in production and on the field. Therefore, to get 5G equipment to market quickly, efficiently and economically, T&M vendors will have to work closely with top-tier equipment makers and the standards authorities to resolve technical challenges and provide T&M solutions that are fit for purpose and have a low cost of ownership.

5G testing scenario

The solutions to 5G testing challenges are both evolutionary and revolutionary. Since both 4G and 5G technologies are based on OFDM, the existing equipment for 4G can often be upgraded, in some cases just with software, to make them suitable for 5G. This is the case with signal generators, and spectrum and signal analysers manufactured by leading T&M equipment vendors.

In other cases, hardware evolution is required. This is the case with, for example, vector network analysers, which are required to have multiport test capabilities to support massive multiple input, multiple output (MIMO). A top-of-the-range 5G analyser can provide support for up to 24 ports in real time, which can be increased to 288 ports using a switch matrix. This is important as massive MIMO antenna arrays typically have 128 antenna elements or more. Simultaneous testing of LTE and 5G terminal devices, necessary for the network architecture favoured by most operators, also requires hardware enhancements, in part because over-the-air  measurement solutions need additional shielded chambers.

That said, where evolution of existing T&M equipment or designs is not feasible, technological revolution is required, such as the introduction of new frequency bands. The implementation of components, chipsets, modules, wireless devices and base stations in the 28 GHz or 39 GHz band requires higher integration density and the use of active antenna systems in order to enable efficient beamforming. The need for low path loss and small size leads to highly integrated printed circuit boards that include antennas, amplifiers and analog phase shifters. As a result, radio frequency connectors are no longer available and OTA test solutions have to be rolled out to replace the existing conducted measurement methods. However, OTA testing at sub-6 GHz frequencies is very difficult as far-field (FF) analysis requires very large chambers measuring 10 metres or more.

An innovative solution to this problem is to make near-field (NF) measurements under FF conditions. At cm-/mmWave frequencies, compact antenna test range (CATR) solutions can be applied, which create far-field conditions in close proximity to the device under test. CATR uses a well-designed and highly accurate produced mirror to realise the NF-FF transformation. The reflector weight significantly increases below-6 GHz operation, since massive MIMO antennas easily reach radiating dimensions greater than 70 cm or 80 cm. The cost, fabrication time and handling of large heavy mirrors become prohibitive. Instead, by using an antenna array, it is possible to create a planar field that allows for a quiet zone of 1 metre diameter within a measurement distance of 1.5 metres, thus enabling more convenient and cost-effective equipment to be used. With the introduction of mMTC and URLLC in particular, 5G can facilitate a whole new range of applications from automated driving to internet of things and cloud robotics. This broadens the field of T&M to encompass additional requirements such as safety and security in situations where reliability, deterministic low latency, authentication and encryption are critical. A T&M equipment supplier with products already in these markets and experience in areas such as cybersecurity and radio monitoring will have much to contribute to 5G testing.

Looking ahead

5G T&M is a rapidly evolving topic. T&M equipment suppliers will need to build on their success and experience in 4G to minimise costs for both themselves and customers. They will have to work with customers as solution partners to enable quick market entry for the latter. Taking an active role in driving the new standards from within the standards bodies, particularly the 3 GPP, will provide advanced insight to facilitate early market access.

By Ramarao Anil, Director, R&D & Application Support (Wirelesscom), Rohde & Schwarz, India