In-depth study: a band war detonated by a 5G millimeter wave

The number of wireless devices and the amount of data they consume increases in equal proportions each year—the annual compound growth rate (CAGR) is 53%. As these wireless devices create and consume data, the wireless communication infrastructure that connects these devices must evolve as well to meet growing needs. 3GPP defines three high-end 5G use cases (Figure 1) with the goal of providing available mobile broadband data anytime, anywhere. However, merely improving the spectral efficiency of a 4G architecture network is not sufficient to provide a step function of the required data rate.

In view of this, researchers are working on higher frequencies and hope to have a viable solution. Early results in channel sounding operations were quite good, so wireless standards organizations around the world realigned their research priorities to understand how the next generation of 5G wireless systems can be integrated and from the use of these new frequencies and higher bandwidths. Benefit.

Figure 1: Three high-end 5G use cases defined by 3GPP and IMT 2020

Define 5G key performance indicators

When designing these use cases, it is hoped that future wireless standards will complement new applications with gaps that are not met by existing wireless standards, and each case requires a different set of new key performance indicators (KPIs). The Enhanced Mobile Broadband (eMBB) defined by the IMT 2020 use case is expected to reach a peak data rate of 10 Gb/s, which is 100 times faster than 4G. According to Shannon-Hartley's law, capacity is a function of bandwidth (spectrum) and channel noise, so the data rate is indeed related to the available spectrum. Since the spectrum below 6 GHz has been allocated, the spectrum above 6 GHz (especially in the millimeter wave range) is an ideal alternative to the eMBB use case.

Millimeter wave: story of three frequencies

To serve customers, telecom operators around the world have invested billions of dollars in the spectrum. Setting the spectrum auction reserve price highlights the market value and the insufficiency of the precious resource. Opening up new spectrum allows telecom operators to not only serve more users, but also provide a more efficient mobile broadband data transmission experience. Millimeter-wave spectrum is not only very abundant compared to the spectrum below 6 GHz, but it can be used with a little authorization, so operators around the world can use millimeter waves. In addition, modern chip manufacturing technology has significantly reduced the cost of millimeter-wave devices, so in terms of price, these devices are already available for consumer electronics. The challenge of using millimeter waves is mainly because these spectrums have not been fully studied and there are still unresolved technical problems.

Telecommunications operators have begun to study millimeter-wave technology to evaluate the frequency range that is best suited for mobile applications. The International Telecommunication Union (ITU) and 3GPP have jointly planned a two-stage study of the 5G standard. The first phase of the study will focus on frequencies below 40 GHz, in order to meet the more urgent commercial needs, the completion time is set to September 2018. The second phase is expected to begin in 2018 and be completed in December 2019 with the goal of achieving the KPIs listed in IMT 2020 and focusing on frequencies up to 100 GHz.

In order to unify the global millimeter-wave frequency standard, the ITU announced a list of recommendations for globally available frequencies between 24 GHz and 86 GHz after the recent World Radiocommunication Conference (WRC):

24.25–27.5 GHz, 31.8–33.4 GHz, 37–40.5 GHz, 40.5–42.5 GHz, 45.5–50.2 GHz, 50.4–52.6 GHz, 66–76 GHz, 81–86 GHz

Shortly after the ITU's proposal, the US Federal Communications Commission (FCC) facilitated the release of the Proposed Specification Announcement (NPRM) on October 21, 2015, introducing new and flexible service rules for the 28 GHz, 37 GHz, 39 GHz, and 64-71 GHz bands.

Figure 2: FCC proposed frequency band for mobile use

When the ITU, 3GPP and other standards organizations decided to use 2020 as the deadline for defining the 5G standard, mobile telecom operators are stepping up their efforts to introduce 5G services. Verizon and AT&T in the US are committed to launching the initial version of 5G in 2017. South Korea plans to launch a 5G trial version in the 2018 Olympics, while Japan is expected to showcase 5G technology at the 2020 Tokyo Olympics. With these different units setting their own targets, the frequency options for 5G are also gradually coming to the table: 28GHz, 39GHz and 73GHz.

There are many reasons why these three bands stand out. First of all, these three frequencies do not have to absorb about 20dB/km of oxygen absorption loss like 60GHz, and their oxygen absorption rate is much lower than this value (as shown in Figure 3), so it is more suitable for long-distance communication. These frequencies also work well in multipath environments and can be used for non-visual distance (NLoS) communications. With high directional antennas combined with beamforming and beam tracking, millimeter waves provide a stable and highly secure connection.

Dr. Ted Rappaport of the NYU Polytechnic School of Engineering and his students have begun to study channel characteristics and potential performance at 28 GHz, 38 GHz and 73 GHz. They explored potential service disruptions at these frequencies by disseminating measurements and research, and have published several related papers. Through the existing data and research of these frequencies, combined with the available spectrum around the world, the prototype of millimeter waves can be performed from these three frequencies.

Figure 3: Atmospheric Absorption Rate in Millimeter Wave Frequency Range (in dB/km)

28GHz

As mentioned above, telecom operators are eager to acquire unallocated large amounts of millimeter-wave spectrum; they will play a key role in influencing the frequencies used in the millimeter-wave spectrum. Samsung performed channel measurements on its own in February 2015 and found that the 28 GHz frequency can be used for mobile communications. These measurements validate the expected path loss in the urban environment—the path loss index in the NLoS link is 3.53, and Samsung claims that the data indicates that millimeter-wave communication links can support distances of more than 200 meters. The study also includes the use of phased array antennas. Samsung also began to perform characterization design, allowing the phone to accommodate sophisticated phase array antennas. In Japan, NTT Docomo teamed up with Nokia, Samsung, Ericsson, Huawei and Fujitsu to successfully complete field tests for 28GHz (and other frequencies).

In September 2015, Verizon announced that its key partners, such as Samsung, will be field tested in the United States in 2016, four years ahead of the proposed deadline for the 5G standard by 2020, making Verizon an advanced player in the 5G market. In November 2015, Qualcomm tested 28 GHz through 128 antennas to demonstrate the performance of millimeter-wave technology in a densely populated urban environment and how directional beamforming can be used for NLoS communications. After the FCC announced that the 28GHz spectrum can be used for mobile communications, further experimentation and field testing are bound to continue. Verizon also announced the lease of XO CommunicaTIons' 28GHz spectrum protocol, which includes the purchase option to buy spectrum at the end of 2018.

However, please note that the 28 GHz band is not on the ITU's list of globally available frequencies, so it is still unclear whether this band will be a long-term frequency for 5G millimeter wave applications. However, based on the availability of this spectrum in the United States, South Korea and Japan, and the early field testing of US telecommunications operators, 28GHz, whether or not it becomes an international standard, may directly become a mobile technology application in the United States. South Korea's goal of demonstrating 5G technology in the 2018 Olympics may also be the first to promote 28GHz technology for consumer products before the standards organization determines the 5G standard. On the other hand, since this frequency is not on the International Mobile Telecommunications (IMT) spectrum list, it has also attracted the attention of FCC members.

US FCC Commissioner Jessica Rosenworcel mentioned in a speech in Washington in February 2016: "When we look far, we will find that some places must be traveled by the United States alone. It contains the 28GHz band...but This band was not included in the discussion at the World Radio Conference (WRC) held in Geneva last year, nor was it listed in the 5G spectrum study list. However, since this band can be allocated to mobile applications worldwide, I think the United States should Continue to explore this new spectrum. Both South Korea and Japan have already begun testing this band, and we can't stop now. We have to move forward alone and complete the architecture for the 28GHz band by the end of the year."

Commissioner Michael O'Rielly even wrote a long article on the blog to express his dissatisfaction with the results of the 2015 WRC meeting to the FCC: "This made me start thinking about what happened at WRC-15 and the actual results it brought. And its subsequent impact on the role of the ITU. These practices are likely to undermine the future value of the WRC and make the ITU more likely to be a tool subject to government and existing spectrum user control, thereby hampering spectrum efficiency and technological progress."

It is still not known whether 28GHz is widely used in 5G applications, but this frequency is absolutely very important at this stage.

73GHz

At the same time as the 28GHz related research is being carried out, the E-band frequency has also attracted attention in the field of mobile communication in recent years. Nokia began the study of this frequency using the 73 GHz channel measurement results of New York University (NYU). At NI Week 2014, Nokia demonstrated its first 73GHz over-the-air (OTA) results through NI prototyping hardware. This system continues to evolve as research progresses and continues to demonstrate new technological achievements through public demonstrations.

At the 2015 World Mobile Communications Conference (MWC), the prototyping system was able to perform more than 2 Gbps of data transmission with lens antennas and beam tracking technology. The system's Multiple Input Multiple Output (MIMO) version was also demonstrated at the 2015 Brooklyn 5G Summit, which can perform data transfers up to 10 Gbps, and in less than a year after MWC 2016, This prototype shows a two-way air transmission link with a transmission rate exceeding 14 Gbps.

Nokia is not the only vendor to show 73GHz results at MWC 2016. Huawei and Deutsche Telekom also jointly demonstrated prototypes that can operate at 73 GHz. This demonstration uses multi-user (MU) MIMO, demonstrating high spectral efficiency and the potential to achieve over 20 Gbps transmission rates for individual users.

Some 73GHz studies have begun and more research is expected in the next three years. One of the distinguishing features of 73 GHz and 28 GHz, 39 GHz is the continuous bandwidth available. A continuous bandwidth of 2 GHz in the 73 GHz is available for mobile communications, which is the most extensive of the proposed frequency spectrum. In contrast, 28GHz provides only 850MHz bandwidth, while in the US, there are two bands around the 39GHz that provide 1.6GHz and 1.4GHz bandwidth. In addition, as described by Shannon's law, higher bandwidth represents a higher amount of data transmission, so 73 GHz has a strong advantage over other frequencies mentioned above.

39GHz

Although the ongoing 38 GHz public study is the least, there is still a chance to be part of the 5G standard. The ITU has listed it as one of the available frequencies worldwide, and according to New York University research, existing channel data can prove to be available frequencies. However, this band has more existing applications than 28 GHz or 73 GHz and is therefore a challenge for the 39 GHz to incorporate the 5G standard. The FCC has applied the proposed spectrum for possible mobile applications to accelerate future US research on this band.

When Verizon embarked on the first 28GHz field test in 2016, it was planned to test 39GHz. In addition to the 28 GHz license, XO CommunicaTIons also offers a large number of 39 GHz licenses. The 39GHz, due to the large investment of telecom operators, and listed in the IMT option, will undoubtedly become one of the candidate spectrums for the 2020 5G standard.

Millimeter wave prototyping

Since the basic properties of millimeter-wave channels are different from current mobile phone models, and there are many unknowns, researchers must develop new technologies, algorithms, and communication protocols to fully exploit the potential of millimeter waves in the 5G field. It is very important to build a millimeter wave prototype, especially at an early stage. The establishment of a millimeter-wave prototype confirms the feasibility of a technology or concept that cannot be achieved by simulation alone. The millimeter-wave prototype can perform communication operations in real-time over-the-air transmission in a variety of scenarios, thereby unlocking the secrets of the millimeter-wave channel and facilitating the application and promotion of the technology.

There are several challenges to building a complete millimeter wave communication prototype. Suppose there is a baseband subsystem that can handle multiple GHz signals. Most LTE implementations today typically use 10MHz channels (up to 20MHz), and the computational load increases linearly with bandwidth. In other words, the computing power must be increased by more than 100 times to meet the 5G data rate requirements. In addition, in order to perform physical layer operations of the millimeter wave system, an FPGA must be used in the prototyping process.

Creating custom hardware with prototyping capabilities for millimeter wave applications is a very difficult task. The millimeter wave frequency is ideal for communication operations due to its large continuous bandwidth. To find an off-the-shelf hardware transmitter or receiver with 1 to 2 GHz bandwidth for 5G application requirements, it is costly, and it is not even possible to find an instrument that meets this condition at some frequencies. Even with this kind of hardware, its ability to configure and process raw data is limited, and may even be completely unworkable. Therefore, designing a custom FPGA processor board has become an attractive solution. It may not take long to design the FPGA board hardware, but if you want to develop a software interface to communicate with it, even the most experienced engineers may take a year or more to complete, and this is just the prototyping system. Part of it.

In addition to the FPGA board, the millimeter wave prototyping system requires the use of state-of-the-art digital-to-analog converters (DACs) and analog-to-digital converters (ADCs) to capture bandwidths between 1 and 2 GHz. Some RFICs on the market currently have chips that can be converted between the fundamental and millimeter-wave frequencies, but these options are limited and mostly only used in the 60 GHz band. The IF and RF phases can be used as an alternative to RFICs. Once engineers have a baseband and IF solution, vendors can offer more options than the fundamental RFIC for millimeter-wave wireless headends, but they are still very limited. The development of millimeter-wave wireless headends requires expertise in RF and microwave design, which is completely different from the technology required to develop FPGA boards, so teams must have multiple disciplines to develop all the necessary hardware.

FPGAs are a core component of a millimeter-wave fundamental frequency prototyping system, and designing multiple FPGA systems that can handle multiple GHz channels will result in a more complex system. To address the system complexity and software challenges faced by telecom operators and communications researchers, NI offers a range of configurable millimeter-wave prototyping hardware, as well as millimeter-wave physical layer source code, which not only explains the fundamental characteristics of the millimeter-wave system's fundamental frequency. It also simplifies data migration and processing for multiple FPGAs, simplifying overall operations. These tools all help to turn new prototypes into systems and products that are critical to the development of 5G technology.

in conclusion

It is unclear how 5G technology will be implemented in the future, but it can be determined that millimeter wave will be one of the technologies. In order to meet the demand for data transmission, a large amount of continuous bandwidth above 24 GHz must be used, and researchers have demonstrated that the millimeter wave technology can achieve a transmission rate of more than 14 Gbps through prototyping. The biggest problem today is which millimeter-wave band is used for mobile communications. The ITU may be able to set a frequency for 5G technology for mobile applications. If a mobile phone only needs a set of (rather than multiple sets of) chips, it can achieve a global communication range, which can reduce the development cost for mobile phone manufacturers and reduce the cost of use for consumers. However, the cost of redistributing existing frequencies is high.

Finding a band that the world agrees to use will be a ambitious goal, but it may not be possible in the end. Due to the tight schedule, local telecommunications operators have chosen to skip the ITU recommendations and directly select those spectrums that are not universally available but are immediately available. They also leveraged the prototyping capabilities to produce prototypes of two-way communication links (a key part of 5G development) through field testing, allowing researchers to demonstrate the new technology and standardize it faster.

Although there are still many unknown problems, it is certain that millimeter-wave technology will be deployed in the future and deployed at an extremely fast speed. A new generation of wireless communication technology is about to debut, and the world is paying attention to how this technology is implemented.

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