Non-Cellular IoT Device Growth Changing WLAN Test Requirements

by Brian Davis, Field Applications Engineer, Anritsu Company

Non-cellular IoT devices are expected to experience such strong growth that they will exceed the number of mobile phones in 1-2 years. In fact, of the 29 billion connected devices forecasted by 2022 (according to a recently published market report by Ericsson), 14.2 billion of them will fall into the non-cellular IoT category.

Many of these non-cellular IoT devices and systems will utilize WLAN technologies. Expanding WLAN applications and the conditions related to IoT environments, as well as their associated quality requirements, create new design considerations for engineers. Devices are using more wireless technologies and antennas year-by-year, increasing their complexity. Therefore, products need to undergo more extensive evaluation during the development and design verification stages.

Conventional WLAN measuring instruments use a dedicated inspection test mode that requires a physical control line connection between the WLAN devices and measurement instrument. Consequently, evaluation results may not be a true reflection of the actual performance because the effect of the internal wireless antennas is not considered.

Accurate verification, while vital, is only part of the equation. Testing must be efficient — both in terms of time and cost — for product success to be achieved. Assuring quality of these diverse and complex devices quickly and economically requires the ability to measure RF performance under actual operating conditions. Single-instrument solutions are now available that can satisfy all these criteria. Engineers need to consider specific features and functionality when selecting WLAN test sets to effectively meet the accuracy, throughput, and cost demands placed on them when bringing non-cellular IoT-based products to market.

Real-world Scenario 

Creating a test environment that simulates a live network is one of the most effective means of saving time and money. To that end, Anritsu Company has developed the Wireless Connectivity Test Set MT8862A (Figure 1). The solution serves as an actual access point to measure the RF conditions for quality assurance of diverse and complex 802.11a/b/g/n/ac devices. A built-in web server establishes a direct connection to a web browser, eliminating the need to install a driver, special firmware, or software from a PC.

Supporting this capability is a Network Mode in the MT8862A, which allows the performance of the target WLAN device under test (DUT) to be measured in its actual operating state. The result is a simpler test environment that eliminates the need for dedicated vendor-provided test modes required by other instruments that conduct WLAN device inspections.

Simplicity 

Ease of use creates a more efficient test environment. Built-in web servers that are controlled by a PC to simplify operation and testing help to improve productivity. The ready-to-use GUI in the MT8862A achieves this, thereby eliminating the need to install control software and version matching between the main unit firmware and control software, as well as OS dependence. System and license updates are made from the web browser GUI to make it easier to maintain the instrument and conduct upgrades as new standards are developed.

Network Mode eliminates the need to synchronize waveforms between the tester and device, as well as the timing associated with pairing the two. Further simplifying testing is the ability of the MT8862A Network Mode to measure RF characteristics with the WLAN devices in realistic operating conditions. It is no longer necessary to put the DUT into a dedicated test mode; the DUT RF performance can be quantified under the firmware conditions at actual shipment.

Measurement Capability

Accurate characterization of WLAN device performance requires test solutions to have key specifications and features. For example, the MT8862A has a wide input level range of -65 dBm to +25 dBm in 0.1 dB steps to support all current WLAN devices. One unit can also support RF Tx/Rx measurements, such as DUT Tx power, Tx modulation accuracy, and receiver sensitivity, for a simple measurement environment.

Given the need for cost and time efficiency, having ports that support output up to 0 dBm streamlines configuring an OTA measurement environment. This is particularly important when measuring the reception power range and receiver sensitivity, such as TRP/TIS, to validate RF performance in WLAN final-use environments.

One MT8862A feature that is beneficial in WLAN device testing is an 802.11a/b/g/n/ac device sensitivity search measurement that outputs a bathtub curve, which eliminates the need for chipset-vendor-provided control software. By using this Network Mode function, DUT performance can be analyzed at high speed for each data rate, offering a convenient measurement solution for verifying compliance with the 802.11 minimum receiver sensitivity test specifications.

With an emphasis on controlling cost-of-test and speeding time to market, engineers should also evaluate WLAN testers based on their ability to show results in a manner that allows for fast analysis. Simultaneous measurement functionality allows DUT Tx measurement results to be shown on multiple displays for side-by-side comparison to reduce troubleshooting time. Real-time numerical and graphical results can be displayed for more efficient performance investigation, as well.

Rx Tests

The MT8862A performs frequency and modulation analyses to measure the Error Vector Magnitude (EVM), which is a sound overall indicator of transmitter quality. When the numerical EVM is bad, the Packet Error Rate (PER) is usually high at the WLAN connection. For this reason, test solutions also need to support the Receiver Blocking test in ETSI EN 300 328 V 2.1.1 for broadband wireless devices operating in the 2.4 GHz ISM band. This test is done easily using the PER measurement function of the MT8862A and an internal signal generator that produces the interference wave.

Tx Verification

WLAN test sets need to support key measurements, including power, modulation accuracy, and frequency error. Graphical displays, such as IQ Constellation, Power Profile, and Spectrum, that make analysis faster and more accurate should also be standard.

Solutions can have dedicated software that can send an ICMP Echo Request to measure acts performed by the DUT. With the software, an ICMP Echo Reply is transmitted from the DUT to test pings and perform Tx measurement under conditions that are closer to actual operation than in a traditional test mode. All transmissions can be measured while transmitting/receiving IP data (Figure 2A/2B/2C).

One key benefit is the ability to conduct real-time Tx measurements during IP data communications. By doing so, greater confidence in product performance can be achieved because DUT RF measurements can be made under actual operating conditions.

Frame Capture

To troubleshoot DUT connections, a solution should capture WLAN frames sent to and received from the DUT. Captured logs can be saved by a PC controller in pcap format for analysis by software such as Wireshark to discover routing issues and analyze the IP packet. This eliminates the need for a separate packet sniffer to capture WLAN frames and supports troubleshooting of WLAN frames in the RF measurement environment.

Conclusion

Engineers designing non-cellular IoT devices and systems require test solutions that can accurately verify products in a time- and cost-efficient manner. Single-instrument solutions that provide dedicated hardware and software offer the tools to meet the criteria and establish a test environment that addresses the demands of a growing market.

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