Exploring the virtual reality of 5G (Part 2)

Article By : Larry Desjardin

Know the test and measurement equipment now available for 5G.

In Part 1, I covered the drivers and application behind 5G mmWave communications. I roamed the halls of International Microwave Symposium (IMS), searching for the business justification for 5G, testing each of the hypotheses. In Part 2 of this series, I look at the test and measurement equipment now available for 5G.
For the record, there are a lot of standard products that could be used in some aspects to test 5G- mmWave network analysers, signal generators, and signal analysers, for example. I'll note that I saw plenty of equipment from Anritsu, Keysight, and Rohde & Schwarz that fit into this category. That's all well and good, but I was looking for more- specific products or systems tackling the unique challenges presented by 5G mmWave. This decreased the number of vendors to three: LitePoint, Keysight, and NI. Each were showing 802.11ax test systems (more on that in a future column), but I wanted to highlight products focused on 5G. Each takes a different architectural approach, which I will highlight as well.

LitePoint
I had no appointment at the LitePoint both, so I just crashed it. I was immediately drawn to a horn antenna I saw in the booth- a telltale sign of mmWave.

LitePoint's 802.11ad test system, including remote RF head and antenna.

LitePoint was showing an 802.11ad test system, also known as the WiGig standard. 802.11ad can be thought of as an advanced generation of Wi-Fi that uses the spectrum near 60GHz to deliver speeds up to 7 Gb/s. The test architecture consists of a box (possibly proprietary modular inside) that generates or analyses the IQ data which is converted at a remote head. The remote head converts the data between mmWave and digital, and includes the horn antennas.
The system is focused on characterisation and manufacturing test of complete WiGig products- which explains the horn antenna. There are no connection points with completed WiGig products, so an antenna over a short distance is the only option.
Try as I could, I did not see any data on this product from the LitePoint website, indicating the preliminary nature of this product. Expect it soon.
My next stop was Keysight Technologies…

Keysight Technologies
The Keysight booth was loaded with interesting demos. While the company supports a number of instrument form factors, it was interesting to see how the modular architectures of AXIe and PXI were dominating so many of their communication test systems.
Before I write further, it's full disclosure time. My consulting company, Modular Methods, is a member of the AXIe and PXI consortiums, and I have been a long-time proponent of these architectures. I also serve as a strategic advisor to the AXIe Consortium, often as the chairperson for technical or marketing committees. Finally, I retired from Agilent, the predecessor to Keysight, a few years ago.
With that out of the way, it was interesting to hear Keysight VP Mark Pierpoint describe the multi-channel nature of new communication technologies at an IMS press event. It doesn't take a rocket scientist to connect the dots to Keysight's rapid adoption of modular platforms to address many of these same applications. Multiple channel applications are tailored made for a scalable, modular approach. As I've pointed out in the past, MIMO actually stands for Modular Instruments Meet Opportunity (though some are determined to hang on to the original meaning of Multiple Input Multiple Output).
So I headed onto the floor to find a demanding application. I found it in the realisation of an 8×8 beamforming measurement system, packaged neatly into a 4U AXIe chassis. Think of it as a 8×8 MIMO system with special application software, all in the equivalent rack space of a PXI chassis. This is approximately double the density found in the densest PXI systems. This should not be surprising, as AXIe allows 2.5 times the circuitry volume in the same 4U rack height as PXI. I have covered other vendors who have achieved similar density improvements in AXIe.

A beamforming measurement system is shown above. Eight channels of 65Gs/s signal generation plus eight channels of 1.6Gs/s digitizing, along with a synchronisation module and embedded controller are integrated into a single AXIe chassis. SystemVue software is used to generate and analyse specific waveforms, often modifying the embedded FPGAs.

Mike Millhaem, 5G Technical Architect for Keysight, led me through the system's operation. Depending on the final application, a user would buy the signal generation portion, the analysis portion, or both.
As I've noted in columns before, 5G must inherently support beamforming to increase the system gain to counter the high attenuation at mmWave frequencies. However, beamforming is also deployed in 802.11ac, 802.11ad, and many cellular MIMO systems. The system Mike showed could be used for any of these, with suitable up or down conversion.
All beamforming systems depend on constructive and destructive interference from signals transmitted on each antenna element. By adjusting the amplitude and phase on each element, a beam (or a null for that matter) is formed. The locations of the peaks and nulls are critical for many beamforming systems. A beam pattern can be created by comparing the signal strength at every potential receiver position.
Keysight's system brings this back into the lab environment. The concept of the test goes like this: A beamforming algorithm is defined in Keysight's SystemVue software. SystemVue generates IQ data which is downloaded into eight high frequency signal generators, which simulate the gain and phase at each of eight elements. The M8195A is a four-channel 65Gs/s AWG (arbitrary waveform generator) that exists as a single AXIe module, so two slots can deliver all eight channels. At 65Gs/s, RF signals up to 20GHz can be created without up-conversion. The M8197A Synchronisation module is used to keep all AWG channels synchronised.
At this point you have created the beamforming algorithm- but how do you test it? In the demo, Keysight uses the M9703A AXIe 1.6Gs/s 8-channel digitizer to capture each of the generated signals, and then to process them exactly like a receiver would- essentially summing up the vectors. However, you need to do the summation quickly for each point in space, both azimuth and elevation. This is done by using SystemVue again to create the vector calculation that will run in the FPGAs embedded behind each digitizer channel. The results are transferred back to SystemVue for final processing and display. An optional PXI down-converter and IF amplifier can be used to analyse signals of higher frequencies.

The images above show the beam pattern measured for a 4×2 antenna array. Azimuth and elevation may be viewed together, or separately. Image courtesy of Keysight Technologies.

Besides the beamforming measurement application, Keysight used the demo to showcase several capabilities. SystemVue FPGA Architect is critical to the signal analysis, and populates the FPGAs on the AXIe digitizer with user-defined DSP algorithms, though operating at hardware speeds. This is something that NI has addressed through LabView FPGA, and Keysight has hinted at doing for some time. Also being showcased was the per channel synchronisation abilities of the signal generators and digitizers, plus their impressive density.
It was time for me to walk to the National Instruments booth…

National Instruments
What was interesting to me was something that NI wouldn't reveal. More precisely, NI displayed a mystery system on the show floor that hinted at things to come. Before I get to that, let me point out a couple systems that were public.
NI showed their recently introduced 802.11ax system, and some interesting developments regarding their PXI-based semiconductor tester. Regarding the latter, NI reported that many customers are now demanding power amps to be tested the way they will be used- with a running DPD (digital pre-distortion) algorithm to reduce effective distortion. I had an interesting chat with David Hall and Charles Schroeder of NI about this. You can debate whether this is needed or not, but if the customer requires it, it's not much of a debate. The issue is that DPD algorithms are slow when performed with software. NI, using LabView FPGA, has developed DPD algorithms that can be downloaded into the FPGAs resident on their PXI instruments (such as the Vector Signal Transceiver). This was shown running within a semiconductor test system testing a RF power amplifier.
Back to the mystery system. Here it is:

What will NI be announcing? The answer lies behind this chassis' faceplate.
Now you know as much as I do! From the title, it claims to be a system capable of 500MHz signal generation and analysis. The chassis has the dimensions and cooling pattern of a PXI chassis, so the hardware products are most likely PXI. I can't tell whether the faceplate and associated connectors (LAN and USB) are representative of the new system or not.
OK, one more clue. This link goes to an NI page where you can "Be The First To Know". The last time NI did something like this, they were introducing the VST, so expect something of major importance. The system isn't real yet. Let's say it's in the virtual reality space.
And, that makes it perfect for 5G.