Q&A with ADI’s Kevin Chuang on 5G challenges

While 5G technology brings benefits like faster data transfers, higher bandwidth and lower latency, it also leads to technical challenges for power and RF design around higher frequencies, power consumption, efficiency and size. In addition, new capabilities like MIMO and carrier aggregation, as well as the different frequency bands from sub-6 GHz to more than 24 GHz in the mmWave spectrum, bring new system design challenges, calling for smaller and more efficient power devices.

Efficiency is one of the biggest challenges, especially as the industry continues to tackle sustainability issues. One trend that we have seen to address this issue and other challenges is the shift to wide-bandgap (WBG) devices, such as gallium nitride (GaN) and silicon carbide (SiC). These devices offer several advantages over silicon, including higher switching speed, higher power density, lower electrical current loss and better thermal management.

Kevin Chuang, senior principal engineer at Analog Devices Inc. (ADI) speaks with Electronic Products about 5G technical challenges and the benefits of WBG technology for RF power. One of his focus areas is accelerating radio technology for next-generation wireless communications, dealing with RF systems and signal processing.

Electronic Products: What are the challenges when deploying 5G networks, and how is Analog Devices helping customers meet some of these 5G challenges? Can WBG technology solve some of these issues?

ADI’s Kevin Chuang (Source: Analog Devices)

Kevin Chuang: Today’s 5G deployment already creates many challenges for mobile network operators, especially when co-locating with the existing networks from 3G and 4G. Our goal at Analog Devices is to promote savings for our customers on capex and opex by leveraging our proven IP to help reduce energy, design time and risk. As an example, our RadioVerse open radio unit (O-RU) reference design platform facilitates more efficient radio deployment that could overcome the fundamental challenges, such as energy efficiency and power consumption. Furthermore, the O-RU reference design platform reduces RF design hurdles with an extensive library of fully linearized WBG-based RF power amplifiers (PAs) catered to all types of base-station deployment needs. In fact, we have worked with various vendors for both GaN-on-SiC and GaN-on-Si technologies on a variety of radio types, including both macro cell and massive MIMO radio units. The adoption of GaN for RF power is already pervasive, as the FR1 market requires higher efficiency and competitive RF solutions.

EP: How do the higher bandwidth and higher frequencies of 5G impact the RF chain, and how does that translate into new requirements and challenges for RF and/or power component design?

Chuang: As you go to higher frequency, maximizing power efficiency in the face of increasing occupied and instantaneous bandwidth becomes more challenging. These wider bandwidths also increase the complexity of linearizing digital pre-distortion (DPD) algorithms. For example, ADI’s fifth-generation DPD, designed for GaN PAs, includes solutions for multiscale time-constant charge trapping, further improving PA performance consistency.

EP: Do 5G radios place new challenges on PAs in particular? And what are those challenges and how are they being solved?

Chuang: Compared with low bands (RF frequencies below 1 GHz), the new requirements and challenges for RF are driven by the demand for increased network capacity and improved network coverage at the expense of using more RF transceivers and antennas. Those challenges are being solved today for 5G by utilizing the midband spectrum between 3 GHz and 4 GHz. With the same aperture and 3× wavelength reduction, the space allowed for the RF front-end design requires use of PA modules without compromising performance, such as power efficiency and linearity. From the system perspective, a single package of integrated multistage amplifiers, matching networks and bias control circuits simplifies the integration of the radio unit.

EP: Does enhanced MIMO performance bring new system design challenges, such as increased demand for smaller and more efficient PAs?

Chuang: To solve the enhanced MIMO design challenges at the system level, radio units must be designed efficiently by investing in energy-saving technologies and features. GaN for RF power is the natural choice of such technology because of its excellent combination of high-power density and high gain-bandwidth cutoff frequency that cannot be attained by the silicon-based RF LDMOS counterpart.

EP: With the first release of 5G Advanced capabilities (especially enhanced MIMO, along with AI/machine learning, extended reality and network energy savings), is it creating challenges for devices like transistors and power amplifiers as well as RF front ends? What are those biggest challenges and what kinds of benefits can WBG deliver in these areas?

Chuang: To understand where the RF technology is relevant in 5G Advanced, we must look into the development that has taken place in the standards organization. 3GPP paves the way for commercialization of 5G. The market as a whole has gone through three releases of 5G technology development since 2018. Enhanced MIMO beamforming technology will be instrumental in the higher end of the FR1 spectrum as well as emerging bands, such as 3GPP N104 between 6,425 MHz and 7,125 MHz. This suggests that the new radio architecture for the N104 band may require 4× as many antenna elements or RF PAs as what we have today between 3 GHz and 4 GHz. For those advanced massive MIMO radio units, sustainability is at the forefront of the technology development.

In real-world base-station scenarios, radios rarely operate at peak capacity, so it is essential to include network energy-saving features. For instance, the micro sleep-mode feature in the radio unit can reduce power consumption during low utilization periods by automatically shutting down resources on the fly. The need to dynamically minimize energy consumption at different load levels is also critical and depends on the traffic-tracking ability of the PA design as well.

EP: What new frequency bands will be important beyond today’s 5G for 6G, and will they pose new challenges?

Chuang: The global telecommunications business sector is a notable source of greenhouse gas emissions. With the demand for mobile data continuing to rise at an exponential rate, not only does the energy efficiency of the next-generation cellular networks need to improve significantly to meet global sustainability targets, but the emerging spectrum will be crucial in supporting new capacity and coverage demands. From the base-station perspective, we need to look out to the emerging frequency bands in the upper midbands between 7 GHz and 24 GHz.

Compared with 3.5 GHz with the same aperture and 4× wavelength reduction at 14 GHz, the industry expects to work with thousands of antenna elements in the radio head, which is an order of magnitude higher than what is today at 3.5 GHz. This advanced massive MIMO requirement in the upper midband expects to provide a capacity-coverage tradeoff suitable for wide area deployments and new opportunities for RF technologies.