With 3GPP set to announce a second set of standards this summer, the 5G wave is rising fast. This acceleration towards pervasive 5G also means the industry is facing a range of complex challenges in order to realize the technology’s full potential.
As the vast array of new services and products are being developed ready to market, they will need rigorous testing to ensure they meet both current and emerging industry standards, and deliver the performance expected of them, says Girish Baliga, marketing manager — Wireless, Digital & Aerospace Defense test at Keysight Technologies.
Emerging infrastructures will need rigorous, seamless and fault free testing to ensure that 5G can deliver on its promises. Margin of error to test next generation wireless technologies is very less and the cost of recall will be very expensive.
Test scenarios have moved from “good-to-have” to “must do”. Building test architectures capable of doing whatever the situation demands will be challenging, because the use cases are hugely diverse.
Endpoints will appear and disappear rapidly, cell-site complexity will grow with network sharing, and even the bandwidth required for the visibility traffic itself will require new ways of thinking – all while supporting data volumes that are orders of magnitude greater than those of today.
Enter the New Radio (NR) for 5G
The 3GPP standards body has been working on the new air interface now referred to as New Radio (NR). A major milestone was the release of the first NR standard, known as the Non-Standalone (NSA) Release 15 specification. “Non-Standalone” means that the 5G network is dependent upon the existing LTE evolved packet core (EPC) network and an LTE “anchor” carrier for control signaling aggregated with an NR carrier for data. The Stand Alone Release 15 using the next generation (NG) core network and NR air interface is due out in June 2018. This phased approach makes a lot of sense for a complex system like 5G.
The wireless network operators are already planning and doing 5G field trials of various forms, including pre-5G implementations. These early trials are mostly focused on delivering broadband wireless to fixed locations, called Fixed Wireless Access (FWA). These deployments not only deliver immediate value to customers but also allow the industry to gain experience with NR and the higher frequency bands.
The goals of the NR specification are very aggressive. Aggressive as in, they cover use cases including very low to very high data rates, low latency, massive machine-to-machine communication, high reliability, low power operation and the works.
“Think about those requirements a bit and you’ll see that they are full of contradictions and engineering tradeoffs. But engineers do what they do and the NR spec handles these conflicting requirements via a new highly scalable orthogonal frequency division multiplexing (OFDM) system. I won’t try to describe the complex system of variable subcarrier spacing, symbol length and timing but it is designed to be very flexible to cover all the desired use cases,” Girish Baliga said.
Moving to Radiated Testing
And, with signal loss being a problem, adding some additional antenna gain can certainly help. At these higher frequencies (shorter wavelengths), phased array antennas will be used to improve the gain and steer it to where we want it to go. To keep cost down and performance up, these compact phased-array antennas are being attached directly to the RF Integrated Circuit (RFIC). This tight integration into the system means the usual output connectors are not available for measurement use. And yes, all measurements will be made Over The Air (OTA). So, it’s time to throw your cables away.
Accurate connected measurements at FR2 can be a challenge, but decades of measurement science work has made them commonplace. Making accurate OTA measurements is a lot harder, introducing a much larger measurement uncertainty. Think many dB of uncertainty instead of <1 dB for connected measurements! In other words, OTA measurements are going to be less accurate than we have become used to – making everything more difficult.
Mobile wireless devices have always operated in three dimensions. The world tends to be configured that way. When a 3G mobile phone changes location, the system just has to track signal strength and make a handover to the right base station at the right time. Now consider a 5G device working at FR2: the variables now include the base station antenna gain, pattern and direction; the behavior of the channel including fast fading and the mobile antenna gain, pattern and direction.
Let’s consider how the User Equipment (UE) makes and maintains a wireless connection. The UE and base station need to find each other by sweeping their antenna beams around in some organized fashion. Once they lock onto beam settings that work, they’ll need to keep updating the beam directions as the UE moves through the network or changes orientation. Especially at FR2 frequencies, shadowing and blocking can be severe. At some point, the UE will need to switch to another base station, causing the cycle to repeat. Beam management is the key, at the UE and at the base station.
The test challenge is made more difficult by this beamforming operation. How do we ensure that the UE can steer the beam appropriately so that the 5G devices will work? Do we need to test in all 3D directions? Or can we just rely on a few key samples to ensure proper operation?
From how good is my signal to where is my signal
For FR1 the question being asked for the last 100 years was “How good is my signal?” But 5G NR at FR2 brings a new paradigm which is “Where is my signal?” since if it is pointing in the wrong direction its quality is no longer relevant.”
These design and test challenges are being worked on every day by Research engineers and other technical experts in the industry. And, these are the among the key areas that need breakthrough innovation for 5G to be successful. Industry is making progress in these areas but there’s still more work to be done.
Takeaways
To properly test 5G systems, it will be necessary to first pick appropriate channel conditions that adequately reflect the environment of choice. This must take into account fast-changing in-channel impairments, as well as numerous sources of blocking caused by the physical environment and dynamic factors such as vehicle and device movement and body/hand blocking. Any realistic test system will have to emulate similar conditions, but do the existing test methods specified by 3GPP6 scale up to mmWave? The answer is a YES as industry test are committed to getting customers on the fastest path to 5G.
