Avichal Kulshrestha
Staff Technical Marketing Engineer,
National Instruments

Changes in Wireless Demand a New Test Approach

The International Telecommunication Union’s (ITU’s) vision for International Mobile Telecommunications in 2020 (IMT-2020) outlines one of the clearest requirements for the range of use cases in future wireless standards. This vision, designed as a framework to communicate the technical requirements of 5G, outlines three distinct use cases. Although these use cases specifically define the requirements of future mobile communication standards, they reflect the changing requirements for technologies like 802.11ad, 802.11ax, Bluetooth 5.0, NFC, and more.

The first wireless use case, Enhanced Mobile Broadband (eMBB), defines the evolution in network capacity and peak data rates expected from a future wireless technology. Specifically, for 5G, the eMBB use case is designed to deliver up to 10 Gbps of downlink throughput, which is 100× that of single-carrier LTE. The second use case, Massive Machine-Type Communication (mMTC), is designed to deliver wireless access to more devices in more locations at a lower cost. By linking together more devices in more locations, mMTC technology will connect traffic lights, automobiles, and even highways in a smart city. The third and final use case is Ultra-Reliable Machine-Type Communication (uMTC). In this scenario, two key requirements of the wireless connection are latency and packet error rates. Imagine a doctor performing remote surgery using a robot connected via wireless. The reliability of the wireless communications link is a lifesaver.

The requirements of tomorrow’s wireless technology are not only driving new wireless standards like NB-IoT, 5G, and 802.11ax but also changing the way engineers design and test mobile devices.

Over the past decade, wireless standards have evolved to use significantly wider bandwidth channels to achieve higher peak data rates. For example, since 2003, Wi-Fi has evolved from 20 to 40 to 160 MHz in today’s 802.11ax. Mobile communication channels have evolved from 200 kHz in GSM to 100 MHz in today’s LTE-Advanced technology. Advanced DPD algorithms often require 3× to 5× the RF signal bandwidth. As a result, instrument bandwidth requirements can be up to 500 MHz for LTE-Advanced (100 MHz signal) and 800 MHz for 802.11ac/ax (160 MHz signal). Many other applications besides wireless test demand wideband instruments as well. For example, wideband radar systems often require up to 1 GHz of signal bandwidth to better capture pulsed signals.

A second critical requirement of next-generation wireless test instrumentation is better RF performance. With higher order modulation schemes and wideband multicarrier signal configurations, the RF front ends of today’s wireless devices must have better linearity and phase noise to deliver the required modulation performance. Because of these requirements, tomorrow’s RF test instrumentation must also deliver better RF performance.

Modern communication standards ranging from Wi-Fi to mobile use sophisticated multi-antenna technology. In these systems, MIMO configurations provide a combination of either higher data rates through more spatial streams or more robust communications through beamforming. Because of these MIMO benefits, next-generation wireless technologies like 802.11ax, LTE-Advanced Pro, and 5G will use more complex MIMO schemes with up to 128 antennas on a single device. MIMO not only increases the number of ports on a device but also introduces multichannel synchronization requirements. To test a MIMO device, RF test equipment must be capable of synchronizing multiple RF signal generators and analyzers. In these configurations, the instrument’s form factor and the synchronization mechanism are critical.

The final requirement of next-generation wireless test systems is that engineers can design them with software. Advanced wireless test applications increasingly require engineers to tailor the behavior of the instrument’s firmware. In these applications, engineers can experience significant improvements in instrument performance simply by moving closed-loop control, measurement acceleration, real-time signal processing, or synchronous device under test control on the instrument itself.

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