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 A significant milestone in the final sprint toward 5G commercialization

 

Last month the 3GPP (Third Generation Partnership Project) approved 5G New Radio (NR) Release-15 standalone (SA) specification, paving the way for commercial introductions later this year.

 

Leading telecom operators, internet companies, and chipset, device, and equipment vendors contributed to this historic moment in 5G.  Release-15 introduces a new end-to-end network architecture enabling many new high throughput and low latency use cases that opens the door to new business models, and an era of everything connected. 

 

Does this mean 5G specifications are done? Not quite.  3GPP is working on additions to the current release and has already started work on phase II with Release-16 expected in 2019. The specifications add new capabilities and technologies that require leading-edge innovations in new designs. I am personally excited about the technology growth and advancements we will see in the next three to five years as the specifications evolve through Release-16 and beyond.

3GPP Release 15 photo by Keysight representative Moray Rumney.

3GPP Release-15 photo, courtesy of Keysight representative Moray Rumney.

 

The December 2017 announcement enabled operators to deploy 5G non-standalone mode (NSA) using existing LTE evolved packet core (EPC) for the control plane.  With the June 2018 Release-15, now 5G can operate in standalone (SA) mode using the completely new 5G RAN (radio access network) and core. This is a significant step forward because now 5G can support the many different use cases envisioned by IMT-2020, including high throughput on the mobile internet and low latency applications.  Enabling technologies such as flexible numerologies, massive MIMO and beam steering, and the use of mmWave spectrum dramatically changes designs of devices and network infrastructure.

 

Operators and network equipment manufacturers are already conducting 5G trials and plan for initial mmWave fixed wireless introductions in select cities later this year, and mobile smartphone services in 2019. Keysight has been working closely with these companies. Satish Dhanasekaran, senior vice president of Keysight Technologies, and president of the Communications Solutions Group (CSG) shared his perspective on the achievement: “We are excited to enable the industry at a threshold of 5G acceleration and commercialization. The completion of the standalone (SA) 5G new radio (NR) specification marks a distinct milestone and offers a playbook for a connected ecosystem to move forward, in making 5G a reality and unlocking huge potential for society. Keysight is engaged with market leaders, contributing to the 3GPP standardization development, and providing scalable 5G test and measurement solutions from L1 all the way to L7.”

 

What’s next? After a brief self-congratulatory pause, the focus quickly turns to work on a late drop of Release-15 planned for later in 2018 to fix some known issues. There is also the lengthy “to-do” list for Release-16 to address some critical challenges including reducing device power consumption, addressing network interference management, enhancing reliability in IoT use cases, and furthering the integration of licensed, unlicensed and shared spectrum into 5G deployments. There’s a long road ahead of us for 5G, and it’s not going to be an easy one. To stay up-to-date on 5G New Radio, check back on this blog or go to the 5G NR webpage to access white papers, webinars, and other informative content on 5G NR.

 

You can get more information about Keysight Technologies 5G solutions here.

Network of lights

With 5G NR release 15 in June 2018, how soon can you expect to see 5G devices operating at mmWave frequencies?  The current buzz is sooner than you expect. 

 

At the recent IMS 5G Summit, I learned about some timelines. Initial mmWave releases are expected to be point-to-point, or point-to-multi-point, but not fully 5G NR compliant. But soon after, in the first half of 2019, operators and equipment makers are planning to introduce 5G devices with mmWave radios in select cities. This poses some pretty significant challenges for designers to produce a mmWave mobile device that meets expected quality of service while traveling through the network. 

 

mmWave isn’t new for wireless communications, but it is new for cellular communications. 5G NR specifies frequency up to 52.6 GHz and new operating bands that open up almost 10 GHz of new spectrum.

 

  • Frequency Range 1 (FR1): 400 MHz to 6 GHz adds 1.5 GHz of new spectrum in frequency bands: 3.3-4.2 GHz, 3.3–3.8 GHz, 4.4–5 GHz.

 

  • Frequency Range 2 (FR2):25 to 52.6 GHz adds 8.25 GHz of new spectrum in frequency bands: 26.5–29.5 GHz, 24.25–27.5 GHz, 37–40 GHz. Initial mmWave targets are 28 GHz and 39 GHz in Japan and the US.

 

mmWave, where there is greater modulation bandwidth, is essential to meeting the extreme data throughput envisioned in 5G mobile broadband. However, establishing a mmWave communication link and tracking a mmWave device through the mobile network will be a challenge. mmWave signals just don’t behave the same as signals under 6 GHz. 

 

5G NR will use technologies like beam steering and new initial access procedures to enable a mmWave communication link, but transmitters and receivers must also be able to produce and demodulate high-quality signals in the device and base station. IQ impairments, phase noise, linear compression (AM to AM) and nonlinear compression (AM to PM), and frequency error can all cause distortion in the modulated signal. Phase noise is one of the most challenging factors in mmWave OFDM systems. Too much phase noise in designs can result in each subcarrier interfering with other subcarriers, leading to impaired demodulation performance.  These issues are even more problematic at mmWave frequencies with wider bandwidths.

 

Evaluating a signal’s modulation properties provides one of the most useful indicators of signal quality. Viewing the IQ constellation helps to determine and troubleshoot distortion errors. A key indicator of a signal’s modulation quality is a numeric error vector magnitude (EVM) measurement that provides an overall indication of waveform distortion. As modulation density increases, so too does the requirement for better EVM.  Shown here is the 3GPP (Third Generation Partnership Project) TS 38.101-1 EVM requirement for 5G UE (user equipment).

 

 

Modulation scheme for PDSCH

Required EVM

QPSK

17.5%

16QAM

12.5%

64QAM

8%

256QAM

3.5%

 

 

Measurements of the overall spectrum are also used to validate the signal’s RF performance.  

 

Test solutions don’t just migrate from sub 6 GHz.  The test equipment needs to operate at the higher mmWave frequencies with wider modulation bandwidths and have better specifications than the device under test (DUT). When designing test solutions, you now need to be even more concerned about issues like adapters and cables, switching, over-the-air test, and system-level calibration. The measurement system needs to perform better than the DUT’s design goals, and a proper system level calibration helps to eliminate uncertainties due to test fixtures and is valuable for very wide bandwidth signals.

 

To find out more about overcoming the challenges of mmWave device design and test, check out this white paper series that looks at many of the challenges you can expect with 5G NR including, the new flexible numerology, mmWave design considerations, MIMO and beamforming, and over-the-air testing challenges at www.keysight.com/find/5GNR.

The 5G vision set forth by IMT-2020 is an amazing thing.  It opens up so many possibilities for consumers, the environment, health and safety, humanity. Virtually every industry will be transformed, and new ones will emerge. The three defined use cases: enhanced mobile broadband (eMBB) to support extreme data rates, ultra-reliable low latency communications (URLLC) for near instant communications, and massive machine type communications (mMTC) for massive interconnects, are foundational to setting the 5G specifications. 

 

The 3GPP is developing standards for radio interference technologies to be submitted to the ITU (International Mobile Telecommunications 2020) for compliance with the IMT-2020 requirements. While these standards are in some ways an extension to existing 4G standards, they really are radically different from what’s in use today.  If the standards are radically different, then it’s not a stretch that the tests required to verify 5G product designs are also radically different.

 

The initial 5G New Radio (NR) release 15 was introduced in December 2017, and the full release is targeted for June 2018.  Release 15 focuses on specifying standards for the eMBB and URLLC use cases. Standards for the mMTC will be addressed in future standards releases. New releases of the standard will continue to roll out over many years. No previous standard has attempted to cover such a broad range of bandwidths, data rates, coverage, and energy efficiency.

 

Some key differences in 5G NR release 15 include:

 

  • Flexible numerology enables scalability – Where subcarrier spacing was fixed to 15 kHz in 4G LTE, it now scales to higher spacings.  Wider spaced subcarriers shorten the symbol period, which enables higher data rates and lower latency for URLLC use cases.  In contrast, with shorter subcarrier spacing, longer symbol periods allow for lower data rates and energy efficiency for IoT, or the mMTC use case.

 

  • mmWave frequencies open up more bandwidth – LTE supports up to six channel bandwidths, from 1.4 MHz to 20 MHz.  These can be combined through carrier aggregation for a maximum bandwidth of 100 MHz.  The initial 5G NR release 15 specifies frequency up to 52.6 GHz with aggregated channel bandwidths up to 800 MHz. Initial target frequency bands are 28 GHz and 39 GHz.  To put this in perspective, these mmWave bands alone can encompass the entire spectrum of the current 3G and 4G mobile communications system.  This additional spectrum is essential to enabling eMBB extreme data rates.

 

  • Massive MIMO to increase capacity – MIMO in LTE uses multiple antennas to send multiple, independent streams of data through the same frequency and time space. MIMO has been shown to increase data rates by making better utilization of the spectrum. With Massive MIMO, the number of antenna elements on the base station is considerably greater than the number on the device. Implementing multiple antennas on base stations and devices will be essential to increasing capacity and achieving the throughput envisioned in eMBB use cases. 

  

New Test Challenges

These new standards will introduce new challenges in test. 

 

Flexible numerology complicates the development of the 5G NR waveforms and introduces many new use cases that need to be tested.  In addition, it also introduces a new levels of coexistence testing with 4G and potentially Wi-Fi.  

 

mmWave frequencies with more bandwidth changes all assumptions about conducted tests.  Due to the higher frequencies and use of highly integrated multi-antenna arrays, tests will now be performed over-the-air (OTA). 

 

Massive MIMO increases the number of antennas, and subsequently the number of beams coming out of base stations and devices.   These beam patterns, whether at sub-6 GHz or mmWave, need to be characterized and validated in an OTA test environment.

 

 Viewing a 256 QAM waveform with antenna pattern

Viewing a 256 QAM waveform with antenna pattern

 

Radically different?  Absolutely. Test solutions must be flexible and scalable so that they cover the

number of use cases, frequencies, and bandwidths, as well as OTA validation. The test solutions must also evolve as the standards evolve.  Check out this article series by Moray Rumney to understand more about how test will change as we move into the next stage of 5G development: The Problems of Testing 5G Part 1.  

5G has so many promises it’s difficult to tell how they all can be achieved.  From extreme data download speeds, to self-driving automobiles, to IoT devices monitoring over many years.  One of the key enablers for these to happen is the flexible numerology recently defined in 3GPP Release 15.  I find this part of 5G fascinating and think it will be a key part of 5G to support a wide range of frequencies and scheduling for many diverse services. 

 

The top five key features of 5G flexible numerology are:

 

1. Subcarrier spacing is no longer fixed to 15 kHz. Instead, the subcarrier spacing scales by 2µ x 15 kHz to cover different services: QoS, latency requirements and frequency ranges. 15, 30, and 60 kHz subcarrier spacing are used for the lower frequency bands, and 60, 120, and 240 kHz subcarrier spacing are used for the higher frequency bands.

 

2. Number of slots increases as numerology (µ) increases. Same as LTE, each frame is 10 ms, each subframe is 1 ms.  Ten subframes to a frame.  In normal CP, each slot has 14 symbols.  As, numerology increases, the number of slots in a subframe increase, therefore increasing the number of symbols sent in a given time. As shown in figure 1, more slots as the frequency increases results in shorter slot duration. 

 

Slot length scales with the subcarrier spacing: slot length = 1 ms/2 μ

 

Numerology

Subcarrier spacing

# slots per subframe

Slot length

0

15 kHz

1

1ms/21=1 ms

1

30 kHz

2

1ms/22=500us

2

60 kHz

4

1ms/24=250 us

3

120 kHz

8

1ms/28=125µs

 

 

 

Figure 1. Slots within a subframe and the associated slot duration time.

 

3. Mini-slots for low latency applications.  A standard slot has 14 OFDM symbols.  In contrast, mini-slots can contain 7, 4, or 2 OFDM symbols.  Mini-slots can also start immediately without needing to wait for slot boundaries, enabling quick delivery of low-latency payloads. Mini-slots are not only useful for low-latency applications, but they also play an important role in LTE-NR coexistence and beamforming.

 

4. Slots can be DL, UL, or flexible. NR slot structure allows for dynamic assignment of the link direction in each OFDM symbol within the slot. With this, the network can dynamically balance UL and DL traffic. This can be used to optimize traffic for different service types.

 

Figure 2. Link direction can be dynamically assigned.

 

 

5. Multiplexing of different numerologies. Different numerologies can be transmitted on the same carrier frequency with a new feature called bandwidth parts.  These can be multiplexed in the frequency domain.  Mixing different numerologies on a carrier can cause interference with subcarriers of another numerology.  While this provides the flexibility for diverse services to be sent on the same carrier frequency, it also introduces new challenges with interference between the different services.

 

Why should you care?  I see it like a multi-lane super highway with lots of control.  These lanes represent the different types of services offered in 5G. You have the fast lanes that are very speedy and can handle a lot of cars.  You have the slow lanes where traffic may be at turtle’s pace. And now, throw in a motorbike that can speed in and out of lanes at any time.  Now you need to be concerned about traffic and possible collisions.

 

Flexible numerology in 5G is much different from numerology found in 4G.  It enables a lot of flexibility, but it also introduces new challenges with the way waveforms are built and managed.  Now you need to consider subcarrier spacing, UL, DL configurations, and bandwidth parts.  The number of test cases explodes, and device designers will need to create and analyze waveforms in the frequency-, time-, and modulation domains, as well as verify the device’s performance on the network with many different numerologies. 

 

If you are interested in learning more about 5G Numerology, I’d highly recommend watching the webinar: Understanding the 5G NR Physical Layer by Javier Campos. It provides lots of information on the new standards and goes into details on 5G numerology, waveforms, and new access procedures.

I was recently reminded of my over-the-air (OTA) experience with 5G channel sounding.  It was like black magic at the time, and now, as it turns out, is vitally important for the success of 5G. 

 

At Keysight, we realized early on that making measurements at millimeter-wave (mmWave) frequencies would be difficult. What we didn’t realize was that there would be so little information in the standards regarding how to test this far along in the development of 5G. The first 5G New Radio (NR) draft specification was released in December 2017. It documents the 3GPP physical layer, but absent are the specifications for the mmWave test environment. That means the chances of getting lost in your 5G OTA measurements goes up dramatically. And that’s where I want to help.

 

Let’s review some of the things you should know about for 5G OTA measurements.

 

Are OTA tests really required?

 

Here’s a question you are probably asking yourselves right about now: is OTA testing really needed? And here’s my answer: ABSOLUTELY!

 

Current sub 6 GHz RF performance tests are mostly done using cables. That changes when you move to massive MIMO in sub 6 GHz or mmWave frequencies. At mmWave frequencies, beamforming antenna technologies are used to overcome higher path loss and signal propagation issues and to take advantage of spatial selectivity by using narrow signal beams. Phased-array antennas, such as those shown in figure 1, are typically highly integrated devices, with antenna elements bonded directly to ICs, making it difficult, if not impossible, to connect and probe. OTA enables test, but it introduces a more challenging ‘air interface’ between the component or device and the base station wherethe imperfections in the air interface need to be accounted for during test.

 

Example mmWave antenna arrays

Figure 1. Example mmWave antenna arrays

 

You Have To Test OTA, But Now What?

 

Okay, so you need to test OTA, but what kind of tests?   The types of measurements for 5G products vary throughout the development lifecycle and are different for an UE versus a base station.  During design and development, RF parametric tests such as transmitted power, transmit signal quality, and spurious emissions are done for radiated transmitter tests.  Base stations add tests such as occupied bandwidth and adjacent channel leakage ratio (ACLR), to name a few.  Beam-pattern measurements in 2D and 3D and beamsteering or null-steering performance tests are also done during R&D.  Conformance testing is also done to ensure the device meets 3GPP minimum requirements. These can be grouped into RF, demodulation, radio resource management (RRM), and signaling tests. This white paper provides an explanation of these tests: OTA Test for Millimeter-Wave 5G NR Devices and Systems.

 

OTA tests are typically conducted in the radiated near-field or radiated far-field region of the antenna system under test. Measurements in the far-field are conceptually the simplest type of OTA measurement and an approved method identified by 3GPP.  A typical far-field anechoic chamber is shown in figure 2.  With the appropriate probing and test equipment, 2D and 3D beam patterns and RF parametric tests can be performed. The challenge is selecting a reasonable chamber that won’t take up your entire lab space. The length of a far-field chamber is roughly determined by 2D2/λ, where D is the diameter of the device being tested.  With this in mind, a 15-cm device at 28 GHz would therefore require a 4.2-m chamber as shown in figure 3. These chambers will be large and quite expensive.

 

Far-field measurement                                                         Figure 2.  Far-field measurement

 

D (cm)

Frequency (GHz)

Near/far boundary (m)

5

28

0.5

10

28

1.9

15

28

4.2

20

28

7.5

25

28

11.7

30

28

16.8

Figure 3. How far is far-field?

 

An alternative for 5G RF tests that is being used by market leaders and is now being considered by 3GPP is the compact antenna test range (CATR). In Figure 4, a CATR uses a reflector so that it looks like the waveform is coming from a long way away. This seems to be a very promising direction for 5G OTA testing, and 5G market leaders are seeing this as a comprehensive and accurate test method.  However, that’s not the case for RRM test where there is no clear solution because of the many open issues due to the dynamic, multi-signal 3D environment with signal tracking and handovers. 

 

    Figure 4. Compact antenna test range (CATR)

 

If We Could Only Tell the Future

 

Yes, I know life would be a whole lot easier if we knew what to expect, but unfortunately the jury is still out on this one. What I can tell you about OTA is that progress is being made. 

 

There are many really smart PhDs working on solutions, but it’s going to take time to get these testing methods into the standards. In the meantime, I solutions coming from market leaders working directly with test vendors to enable OTA tests of the first 5G devices and basestations. These OTA test solutions are the ones to watch, as they will pave the way for the standards.

 

If you are looking for more information on 5G OTA testing, then I highly recommend watching Malcolm Robertson’s video: Testing 5G: OTA and the Connectorless World or reading the : OTA Test for millimeter-Wave 5G NR Devices and Systems white paper. Looking forward, I’ll keep you posted on important 5G topics and developments in future blogs.