Higher-order QAM and smarter workflows in VSA 2023

3GPP Release 17 and 802.11be (Wi-Fi 7) extend modulation complexity, raising the bar for conformance testing and test instrumentation to new levels. The latest release of Keysight PathWave 89600 Vector Signal Analysis 2023 (VSA 2023) software takes on higher-order QAM and smarter workflows, many customer-requested, for advanced signal analysis. We’ll focus on four areas of enhancements: 5G NR (and, for research, 6G) measurements, cross-correlated EVM, multi-measurements combining EVM with ACP and SEM, and event-based user actions.

Accelerating 5G, O-RAN,  and 6G research

In tracking the 3GPP specification and aligned specifications such as O-RAN WG4 fronthaul and leaning into 6G research, Keysight’s objective with the 89600 VSA is accelerating complex RF system research and development workflows. A visual example shows the range of measurements possible from one IQ data acquisition.

3GPP Release 17 brings 1024QAM, a much denser constellation than the 256QAM in previous releases. The VSA 2023 release supports I/Q reference values (all zeroes or PN23) for PDSCH EVM calculations, avoiding the problem of obtaining “ideal” constellation points from estimation in high noise or system impairments.

Another enhancement for 5G NR in the VSA 2023 release is expanding component carrier views. Even though the 3GPP specification still calls for 16 component carriers, researchers are exploring using up to 32. VSA 2023 users can display data from 32 component carriers with a simple pull-down menu, allowing a side-by-side view of all component carriers for easier performance comparison.

With design teams already looking ahead to 6G but its specifics still in flux, Keysight has also incorporated user-defined constellations and modulation formats in VSA 2023. “We’re trying to be as aggressive as we know how about 6G research topics,” says Raj Sodhi, Keysight 89600 VSA Product Manager.

Several dBs of improvement in EVM measurements

EVM is a critical spec for 5G NR, Wi-Fi 7, and other advanced wireless systems. “If we could get 3 to 5 dB better in EVM measurements, who would care? The answer is everyone,” says Sodhi. With higher-order constellations and broader bandwidths, margins are already tight. For accurate EVM readings, test equipment needs to be distortion-free and much quieter than the specification by a substantial margin.

Cross-correlated EVM (ccEVM) is a Keysight algorithm that eliminates instrument-induced uncorrelated noise using two independent analyzer channels, lowering the EVM noise floor. Depending on how many points the ccEVM measurement in VSA 2023 uses, improvements of 5 dB or more are straightforward, and theoretically, up to 20 dB improvement is possible.

Conformance test peace of mind with smarter workflows

While EVM defines system performance, two other specifications are essential in conformance testing: adjacent channel power (ACP) and spectral emission mask (SEM). Until the VSA 2023 release, RF system designers had to bring several instruments and spectrum analyzer software applications, each with their own setups, to get all three measurements. “Now, we’ve brought ACP, EVM, and SEM under one roof,” says Sodhi.

A new measurement application in VSA 2023 has ACP and SEM presets for 5G base station conformance tests. But it is flexible, allowing measurement configuration for any signal type. It formalizes support for single and multi-carrier ACP, EVM, and SEM measurements from single or sequential acquisitions depending on the hardware IF bandwidth.

This capability leads into “contexts” – a simple setup for 5G NR conformance tests. One setup can support all test models, bandwidths, numerologies, and more.

Advanced triggering with event-based actions

Often, setting up a complex VSA measurement is just the beginning of capturing data. Signal conditions can change rapidly during normal system operation, throwing test results out of whack. A good example is a system with kinematics, such as a satellite in a 5G non-terrestrial network (NTN), where Doppler shift can cause enough frequency error to pull the VSA out of sync during capture.

To cope with this scenario, VSA 2023 adds event-based actions. Users can choose a metric – such as frequency error, EVM, or any data source in a summary table trace in the VSA – and set a condition to monitor. When the condition is met, one of two actions can occur: pause the measurement or run a macro.

In the 5G NTN example, when the Doppler shift drives the frequency error over the selected condition of 10 kHz, a macro runs recentering the VSA on the shifted frequency, continuing the capture seamlessly. A macro can be essentially any set of commands for the VSA, for example, automating a setup change, saving anomalous data to a file, adding markers to zoom in traces, and so on. Advanced triggers based on measurements become possible without extensive experiments to find the right combination of settings.

More enhancements for wireless connectivity

Three more features round out the VSA 2023 release, including some designed for teams working in 6G research.

• Wi-Fi 7 (802.11be) teams are dealing with even higher-order modulation in the form of 4096QAM. Similar to the situation for 5G NR and 6G, pulling ideal constellation points out of noise and impairments can be problematic. Users can specify reference symbols for more accurate EVM measurements. Also, the VSA now automates CRC checking by decoding the PHY Service Data Unit (PSDU).
• UWB changes keep pace with the FiRa specification, with a Keysight engineer now helping drive specification updates. Pulse shaping is computed per the specification in the Baseband Pulse Mask trace, and the Frame Info trace results are enhanced. Synchronization improvements help capture results from multiple UWB frames.
• FlexFrame now includes an adaptive equalizer, increasingly crucial as channel bandwidths grow and impairments make EVM measurements more difficult. Flex Frame continuously evolves the channel estimation with a least mean squares (LMS) algorithm in time domain and a zero-forcing algorithm in frequency domain. For 6G research, an XCorrelation equalization mode, equalizer filter track or hold, and LMS algorithm speed improvements offer more stable equalization.

Discover more about PathWave 89600 VSA 2023

“VSA has been the spearpoint of signal analysis technology, especially for EVM measurements,” says Sodhi. “Often, customers would start with the VSA, then migrate to spectrum analyzer applications for coverage of out-of-band measurements. With the VSA 2023 release, they can start with VSA and stick with VSA for measurements like ACP and SEM – a better workflow using the same measurement science.” Here are some resources for discovering more about higher-order QAM and smarter workflows in the PathWave 89600 VSA 2023 release.

Web page:

What’s New in 89600 VSA?

Videos:

89600 VSA Software PowerSuite Demo for 5G NR ACP and SEM Measurements

802.15.3d Signal Analysis using the 89600 VSA’s Adaptive Equalizer in FlexFrame

Event-Based User Actions in the 89601200C VSA Base Platform

5G Transmitter Validation using PathWave System Design and 89600 VSA Software

Press release:

Keysight Accelerates RF System Design and Digital Mission Engineering Workflows for 5G Non-Terrestrial Networks

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