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The emergence of 5G mobile communications is set to revolutionize everything we know about the design, testing, and operation of cellular systems. The industry goal to deploy 5G in the 2020 timeframe demands mmWave over-the-air (OTA) test solutions and requirements in little more than half the time taken to develop the basic 4G MIMO OTA test methods we have today.

 

If you highlight anything from this blog post, know this:

 

We are going to have to move all of our testing to radiated, not just some of it like we do today, and that's a big deal.

 

 

First, a bit of background on the move from cabled to radiated testing, and then I’ll discuss the three main areas of testing that we're going to have to deal with: RF test, demodulation test, and radio resource management.

 

Millimeter-wave devices with massive antenna arrays cannot be tested using cables because there will be no possibility to add connectors for every antenna element. The dynamic (active) nature of antenna arrays means it isn’t possible to extrapolate end-to-end performance from measurements of individual antenna elements. So yes, for testing 5G, it really is time to throw away the cables…whether we want to or not!

 

A new radio design starts with the reality of the deployment environment, in this case a mmWave one. How this behaves isn’t a committee decision, it’s just the laws of physics. Next, we model the radio channel and once we have a model, we can design a new radio specification to fit the model. Then, we design products to meet the new radio specifications, and finally we test those products against our starting assumptions in the model.

 

If we have got it right—in other words, if the model is sufficiently overlapped with reality—then products that pass the tests should work when they are deployed in the real environment. That's the theory.

 

This process works well at low frequencies. For mmWave, however, there is a big step up as the difference in the propagation conditions is enormous.

 

Now let’s look at the categories of radio requirements that we're going to have to measure—that is, what we measure and the environments we measure them in.

 

For RF, it’s about what is already familiar—power signal quality, sensitivity—and those are all measured in an ideal line-of-sight channel.

 

With regards to demodulation, throughput tests will be done in non-ideal (faded) conditions as was the case for LTE MIMO OTA. There we had 2D spatial channels, but for mmWave, the requirement will be 3D spatial channels because the 2D assumptions at low frequencies are no longer accurate enough.

 

Radio resource management (RRM) requirements are about signal acquisition and channel-state information (CSI) reporting, signal tracking, handover, etc. That environment is even more complicated because now we’ll have a dynamic multi-signal 3D environment unlike the static geometry we have for the demodulation tests.

 

Opportunities and Challenges

 

The benefits of 5G and mmWave have been well publicized. There's a lot of spectrum that will allow higher network capacity and data rates, and we can exploit the spatial domain and get better efficiencies. However, testing all of this has to be done over the air and that presents a number of challenges that we have to solve if we're going to have satisfied 5G customers.

 

 

 

We know that we're going to have to use active antennas on the devices in base stations, and those are hard to deal with.

 

We know that spatial tests are slower than cabled, so you can expect long test times.

 

We've got the whole issue of head, hand, body blocking on devices—it's something that isn’t being considered for release-15 within 3GPP but will still impact customer experience.

 

We know that OTA testing requires large chambers and is expensive.

 

We know OTA accuracy is not as good as cabled testing—we're going to have to get used to that.

 

Channel models for demodulation and RRM tests haven’t been agreed upon yet, which is impacting agreement on baseline test methods for demodulation and RRM.

 

Takeaways

 

There's a paradigm shift going on because of mmWave. We used to work below 6 GHz and the question we asked at < 6 GHz frequencies was, "How good is my signal?" That question led to the development of non-spatial conducted requirements. The question now for mmWave is, "Where is my signal?" That's going to lead to the development of 3D spatial requirements and OTA testing. This is a fundamental shift in the industry.

 

It’s going to be a tall order…testing 5G mmWave devices.

 

Keysight is committed to getting our customers on the fastest path to 5G. Stay tuned as Keysight continues to roll out 5G testing methodologies and system solutions. Meanwhile, explore the 5G resources currently available.

 

Follow our Next Generation Wireless Communications blog and connect with our industry and solution experts as they share their experiences, opinions and measurement tips on a number of cellular and wireless design and test topics that matter to you.

Moray

The London 5G debates

Posted by Moray Employee Nov 18, 2016

Following on the theme from Roger’s recent post Blessings and Curses: Firsthand Commentary on the State of 5G Wireless Conclaves, I was invited to take part in one of the most enlightening 5G events I’ve encountered. It was the first of two 5G debates in London organized by Cambridge Wireless, a UK-based community bringing the mobile wireless community together to solve business problems.

 

The debate took place in the prestigious “Shard” building in central London and was chaired by Prof. William Webb, last year’s president of the Institute of Engineering and Technology. One of the things that distinguished this debate from so many others is that it was a stand-alone event, attracting a diverse audience not typically seen at industry conferences (e.g., the ones in which debates are often curtailed just when they get interesting). The three other panelists alongside myself were Howard Benn, Samsung’s head of standards and industrial affairs; Paul Ceely, head of mobile strategy at British Telecom (which recently bought operator EE); and Joe Butler, director of technology at UK regulator OfCom and, for this debate, representing the UK’s National Infrastructure Commission, which is tasked with planning the UK’s critical infrastructure.

 

The theme of the first debate was What’s left for 5G now that 4G can do IoT and Gbits/s speeds?” while the second had a business focus: “Will operators see increased ARPU from 5G?” A short video of the first debate and a full transcript is available here and the second debate is here.

 

Each panelist gave a short opening statement. Given the recent political environment in the UK, I led with the good news that “5G will be much easier than “Brexit,” and this raised the first of many laughs in what was a good-natured but insightful debate. I gave my reasoning that we have engineers who actually understand 5G whereas the world of politics and economics is populated with those who get by with subjective opinion. That said, I pointed out there is a lot of noise in this 5G space so it is important to know the credentials of those giving advice: are they based on commercial self-interest and hype or are they based on observation of reality backed by physics? After all, at the end of the day, 5G has to work before it can be commercially successful.

 

The debate covered a number of areas in sub-6 GHz territory, through to millimeter-wave developments, IoT and network evolution with NFV and SDN. But the key moment for me started when Joe Butler described his frustration with current infrastructure: “If I get on the train from Brighton to London, which I do on a very, very regular basis, I would dearly love to be able to make a phone call that lasted longer than 30 seconds!” After the laughter died down, the chairman used the opportunity to conduct one of many quick polls of the audience. In this one he asked for a vote in favour of 10 Mbps ubiquitous connectivity vs. delivering blindingly fast, 100 megabits (or even gigabits) a second in pockets of places and also some super low-latency services. The answer to the first question was spontaneously unanimous as can be seen in the picture below captured from the video.

So this means the second debate on the 5G business case will not be short of opinions.

 

The next opportunity for me to interact with the wider 5G community will be at an upcoming IWPC workshop in San Jose hosted by Verizon and focused on the role millimeter-waves will have in 5G. On this occasion I will be delivering a high-level technical paper called “Modelling what matters” that will ask important questions about the focus of current research into 5G. In particular, what concerns me is whether there is sufficient research targeting the design and test of 5G “new radio” to mitigate the spatial dynamics of millimeter-wave radio propagation. More on that later…