By: Sarah Yost, mmWave Product Manager, National Instruments
Everywhere you look today, 5G is at the center of conversations about exciting new technology. Recent announcements from Mobile World Congress 2017 in late February indicate that 5G is already here. The truth is that 5G isn’t here yet, but we are getting closer. The past year has been busy in all aspects of the communications community, from the work on the standardization process to updates from regulatory bodies to our understanding of the channel for new proposed millimeter wave (mmWave) frequencies to the new technology under development that will turn 5G into a commercial reality. Last year, I wrote a paper called “mmWave: The Battle of the Bands” to provide an overview of the technologies being proposed for mmWave frequencies. This year, I’m building on that information by examining mmWave for communications and presenting an update to the question on everyone’s mind: What is 5G and when will it be here?
5G Frequencies: A Combination of mmWave and Sub-6 GHz
Though some things at this point on the 5G journey may not be clearly defined, one thing is certain: sub-6 GHz spectrum is still very important, and mmWave frequencies will be used to supplement sub-6 GHz technology. Figure 1 shows the wide range of requirements expected of 5G, from ultra-reliable, high-bandwidth communication for enhanced mobile broadband (eMBB) applications to the low-bandwidth, machine-to-machine (M2M) type communications we expect to see in Internet of Things applications. It is difficult, if not impossible, for one band of spectrum to meet all these needs, but combining two bands provides complementary coverage. Sub-6 GHz spectrum offers better propagation and backward compatibility for narrowband applications, while the contiguous bandwidth at mmWave frequencies enables the key eMBB applications that 5G promises.
Figure 1: Targeted 5G applications include enhanced mobile broadband and machine-to-machine communication.
The ITU has defined two phases of research: Phase 1 for sub-40 GHz and Phase 2 for sub-100 GHz. Phase 1 is scheduled to end in June 2018 to correspond with the 3GPP’s LTE release 15. Phase 2 is slated to end in December 2019 to correspond with LTE release 16. Figure 2 shows both the ITU and 3GPP timelines as of fall 2016.
Figure 2: ITU and 3GPP Timelines for 5G. Image source: https://frankrayal.com/2016/08/08/will-5g-be-the-last-g/
The ITU’s proposed dates and the frequencies that will be used, however, are anything but certain. At the March 2017 3GPP RAN plenary meeting (#75), a way forward (WF) was presented with an accelerated schedule for the release of 5G new radio (NR), as seen in Figure 3.
Figure 3: Accelerated 3GPP NR Release Schedule (as of March 2017)
NTT DOCOMO presented its recommendation for which frequency bands should be used at the last RAN4 meeting (#82) in a WF. Table 1 summarizes the frequency ranges and corresponding telecom operators.
Table 1. Proposed New Radio (NR) Spectrum Way Forward from RAN4 Meeting #82, Recommeded to RAN Plenary #75
The work at 28 GHz has dominated the news on sub-40 GHz research over the past year, but it is not the only frequency under consideration. The FCC and Verizon have been driving the work at 28 GHz. To allocate additional mmWave bands for flexible use and future proposed rulemaking, the FCC approved the Spectrum Frontiers Proposal in July 2016. The 28 GHz band is one of the three bands available today for flexible use in the United States . Figure 4 presents a visual of the bands. Based on the WF at the RAN4 meeting, global carriers, including European operators Orange, British Telecom, and Telecom Italia, have established significant alignment around 24–28 GHz. This may seem surprising based on previous conclusions that 28 GHz is not a suitable band for Europe because of frequency incumbents, but the lower frequencies in that band have potential. And, as expected, those same European operators are requesting spectrum at 32 GHz.
Figure 4: mmWave Bands Allocated by the FCC
Verizon secured a license for the 28 GHz band from XO Communications last year, and has been vocal about its desire to use this frequency for its initial deployment. In December 2016, Verizon applied for a Special Temporary Authority license from the FCC to conduct market trials in Massachusetts, Michigan, New Jersey, and Texas from January 2 to June 2, 2017. Despite not having a fully standardized version of the technology to roll out for this testing, Verizon is taking a gamble that the hardware they deploy now will be capable of running whatever specification is eventually released through a software update in the future . Other US carriers have agreed to use the 28 GHz band. AT&T and T-Mobile both indicated that they will conduct more research on 28 GHz based technologies and partner with equipment providers for additional field trials.
Verizon is aware that it will push out mmWave technology prestandardization. It has proposed its own specification, referred to as “Verizon 5G wireless technology” or “V5G” in this paper, for the initial deployment. The biggest difference in V5G and NR is the application focus. V5G is limited to fixed wireless access at 28 GHz, but NR is targeted at all communications applications (fixed and mobile) for all frequencies. V5G is intended to deploy a high density of mmWave base stations (think small boxes mounted to telephone poles) that will communicate with commercial box set user equipments (UEs), like a cable box or modem. These UEs will be placed in the consumer’s home or office and will not, for the most part, be moved. The channel will still fluctuate due to a changing environment from movement created by people, animals, cars, rain, and other factors. To address this, V5G is implementing slow beam management that can change the directionality of the beam to ensure the strongest signal between UE and access point regardless of environmental conditions. The question looming over V5G is whether it will comply with 3GPP 5G standards. Verizon is gambling that the hardware it deploys now will be capable of running the finalized 3GPP specification through a software update in the future. If the gamble pays off, Verizon will have a significant head start in the race to 5G. If not, it will have to replace a lot of outdated hardware.
NR is intended to cover all applications and all frequency bands, including the three main application key performance indicators for 5G put forth by the ITU: eMBB, Ultra Reliable Low Latency Communications (URLLC), and Massive Machine Type Communications (MMTC). That means that the physical layer needs to be flexible enough to generate significantly higher data throughput while allowing for hundreds of times more devices to connect to the network for Narrow Band IoT (NB-IoT). The PHY also needs to be reliable enough with low enough latency to be used in self-driving cars. This is no easy task, and the standards that are being proposed for NR are significantly more complex than V5G. Certain aspects like adding beam management are similar between the two, but NR will incorporate both slow and fast beam management. NR will also leverage LTE as much as possible, but it uses different sample and subcarrier rates.
Despite the buzz around NR and a desire to finalize the standard earlier than initially planned, not much data has been published about the performance of the specification. The limited trials at 28 GHz have focused more on channel sounding than demonstrating the feasibility of the NR specification. NI has developed a New Radio prototyping system that can run a multi-user MIMO link. This system uses the NI mmWave Transceiver System (MTS) and flexible physical layer IP written in LabVIEW. The MTS is a modular mmWave software defined radio (SDR) that can be outfitted with different radio heads to support different frequencies. The NR prototyping software has been demonstrated using 28 GHz radio heads from NI and a phased array antenna from Ball Aerospace and Anokiwave. This IP is intended to provide NR researchers with a starting point they can customize and build on to prototype real-time over-the-air NR communications systems.
A 2018 Finish Line for the Race to 5G
By early 2018, we will likely have an answer to “What is 5G?” Based on the accelerated schedule presented at the March 2017 3GPP RAN plenary meeting (#75), the physical layer and MAC layer for NR will be settled by the end of 2017. Frequency selection does not have a strict deadline, but operators are pushing technology forward to get 28 GHz hardware deployed in 2017 in field trials. By the second quarter of 2018, South Korea will have demonstrated its 5G technology preview. The full standardization process will not be complete yet, but a clearer picture of what 5G is will be emerging every day. The race to define 5G may be ending, but the process to design and deploy 5G technology is just beginning. Visit ni.com/5g to stay up to date on NI’s 5G technology news.
 Use of Spectrum Bands Above 24 GHz for Mobile Radio Services, GN Docket No. 14-177, Notice of Proposed Rulemaking, 15 FCC Record 138A1 (rel. Oct. 23, 2015).