Navigating 5G’s Choppy mmWave Surf

2021-05-21  |  6 min read 

There is certainly nothing easy about 5G wireless communications technology. That said, most engineers will tell you that there is a pretty clear increase in complexity in 5G’s Frequency Range 2 (FR2) compared with Frequency Range 1 (FR1).

The Third Generation Partnership Project (3GPP) defines FR2 as between 24.25 GHz and 52.6 GHz. The bulk of FR2 resides in the millimeter-wave (mmWave) spectrum, which is the band of spectrum between 30 and 300 GHz.  

Most of most appealing attributes that are anticipated to come from 5G — massive speed increases, tons of bandwidth, ultra-low latency —are expected to be derived from FR2. Higher frequencies are very efficient for sending large amounts of data, and the available bandwidth means lightening fast upload and download speeds. 5G’s most promising new use cases will almost exclusively owe their existence to FR2.

But we all know there is no such thing as a free lunch. To get the rich benefits of FR2, engineers must grapple with the downsides of mmWave, including poor signal propagation, increased signal noise, lower signal to noise ratio (SNR), and other impairments that affect signal qualify such IQ modulation errors, phase noise, distortion, amplitude, and phase linearity. For test engineers, all of these drawbacks make it more difficult to do the accurate signal analysis required to get a true picture of the performance of the device under test.

The good news is that 5G deployment is accelerating, and that 5G has now been deployed in nearly 30,000 sites worldwide. But the bad news is that the vast majority of these deployments to date have been FR1 deployments. We are just at the very beginning of the commercialization stage of FR2.

Fortunately, modern signal analyzers such as Keysight’s N9042B UXA offer both hardware and software flexibility to enable engineers to overcome the challenges associated with mmWave test and measurement. This flexibility enables users to respond to different input signals of varying power levels, SNRs, and modulation type.

Largely because of the poor propagation characteristics of mmWave signals, they are prone to excessive path loss which makes them more susceptible to noise. To make matters worse, due to the tightly integrated nature of mmWave devices, they lack probe points and thus require radiated test, also known as over-the-air (OTA) test. Wideband signals are also inherently prone to susceptible to higher noise levels because the energy from the signal is spread across its entire bandwidth.

All of these factors mean more noise, which lowers the SNR. And lower SNR makes measuring accurately for things like spurious emissions, error vector magnitude (EVM), and adjacent channel power ratio (ACPR) challenging.

In addition to wide analysis bandwidth and deep dynamic range, the N9042B UXA offers a range of RF signal path options to help test engineers overcome these issues by lowering noise, improving sensitivity, and reducing signal path loss for a better SNR. Typical options include a default signal path for low-level signals, a microwave preselector bypass path for analyzing wideband vector signals, a low noise signal path for making EVM measurements and other measurements that test transmitter modulation quality at higher power levels, and a full-bypass signal path for signals that have a very low SNR. The choice of signal path is typically dictated by the type of measurement and signal you are measuring.

Signal analyzers also offer additional hardware and software flexibility for optimizing the test setup. For example, choosing the optimum levels for the mixer and digitizer is critical to improving EVM measurement accuracy, as is choosing the optimum phase noise configuration. Again, signal analyzers such as the N9042B UXA offer multiple options to configure the test system to the specific measurement and signal.

While mmWave technology holds the key to 5G’s massive potential, mmWave signal analysis is clearly no day at the beach. Fortunately signal analyzers like Keysight’s N9042B UXA, as well as accessories like the V3050A advanced external frequency extender and the U9361 RCal receiver calibrator offer test engineers both the capability and flexibility to accurately measure and understand the true performance of mmWave devices.   

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