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The next transformation in cellular networks, 5G Advanced, will bring higher bandwidth, lower latency and higher energy efficiency to applications like enhanced mobile broadband, massive IoT and edge computing. While these are big benefits for mobile network operators, it is causing RF and component design challenges.

“There will be some new challenges in RF front-end [RFFE] component design for infrastructure due to increased instantaneous bandwidths and higher-frequency bands in FR3 that may be used to meet the ever-increasing bandwidth needs,” said Jeff Gengler, director of RF applications engineering at Qorvo Inc.

“On the component design side, increased integration within modules will significantly help address optimization and consistency of performance over more challenging specifications,” Gengler added. “Increased integration allows for more of the combined system to be tested and validated by the component provider. Integration decreases the size of the solution, which helps reduce cost and helps meet requirements for tighter array pitch at higher frequencies.”

GSMA’s latest Global Mobile Economy Report forecasts that 5G adoption will hit 17% in 2023 and increase to 54% by 2039, representing about 5.3 billion connections. This also means that 5G adoption will overtake 4G by 2029.

The 3GPP Release 18 is the first release of the 5G Advanced standard, delivering new features aimed at improvements in speed, coverage and power efficiency. It addresses the need for greater energy efficiency in 5G networks, along with the growing role of AI/ML and extended reality across applications. It also tackles advanced sidelink and positioning along with enhanced multiple-input, multiple-output (MIMO) radio antenna performance.

5G Advanced power challenges

The new features and enhancements in 5G Advanced translate into challenges at the component level, particularly for RF power amplifiers (PAs).

“New 5G Advanced capabilities and the added features in Release 18 highlight two key areas of need for the power amplifier,” said Eric Westberg, director of product management for integrated power solutions at NXP Semiconductors. “First, it increases the need for innovation in the traditional power-amplifier requirements of higher performance, especially efficiency, bandwidth and smaller size.”

Westberg said these requirements continue to be critical to meet the size and energy-savings needs of operators.

The second area focuses on finding ways for the PA to work more closely with the advanced features in the system, he said. “This has started with the inclusion of controller capability in the PA for massive MIMO [mMIMO] systems. We expect this trend will grow to enable more advanced features in the future to enable more efficiency ratios in backoff conditions and in a wide range of frequency use cases.”

Westberg said there is debate in the industry about the right level of integration. “The inclusion of the controller is in production, and the general trend is toward higher levels of integration.”

At the same time, energy consumption is a challenge that needs to be considered, especially in the PA.

“Energy-efficiency improvements have always been a key metric for infrastructure equipment, and there has been continual advancement in efficiency from device technology to circuit design,” Gengler said.

“On the RF chain, new PA architectures are being proposed to improve bandwidth and efficiency relative to the workhorse Doherty architecture that the industry uses,” he added. “The Doherty PA still has some legs, though, and innovation continues to push bandwidth and efficiency higher. At the system level, power management has been used to reduce power consumption according to traffic loading.”

The sustainability of mobile networks is important for both environmental and operational cost reasons, said Peadar Forbes, director of radio platform development at Analog Devices Inc.

“Within 5G Advanced, we expect to see 3GPP develop energy-consumption models for the radio access network, and this will guide a variety of techniques to modulate the energy consumption of the network in concert with the traffic load,” Forbes said. “Analyzing the tradeoffs between energy consumption and network performance will help identify best-case scenarios based on local network requirements.”

The PA consumes the majority of the energy in the radio, Forbes added. “Turning off unnecessary channels and powering the PA on and off dynamically will be a large part of bringing energy consumption down.

“This has the potential to place some additional requirements on PAs in terms of dynamic operation and, of course, the digital pre-distortion [DPD] loop that linearizes those PAs,” he added. “In the RF transceiver, again, powering up and down both transmit and receive channels more dynamically will be important.”

Performance tradeoffs require innovation

Like any new design, there will be performance and size tradeoffs. For 5G Advanced, it is finding the right balance between higher-bandwidth and higher-energy–efficiency capabilities, which have an impact on the RF chain.

Westberg said the increased bandwidth of today’s networks puts more pressure on engineering solutions to maintain or even increase the efficiency of the system.

One solution is the use of multi-chip modules (MCMs), which allows PA manufacturers to leverage the best features from the different semiconductor technologies to achieve the right balance of performance for the application.

MCMs are one solution for PAs used in mMIMO systems, Westberg said. “MCMs allow a mix of technologies to be used in a compact form factor. For example, LDMOS and GaN [gallium nitride] can be used in a single PA solution to provide 400-MHz solutions for the 3.6-GHz spectrum needs.”

In addition, the MCM allows internal matching and reduces the complexity of radio solutions, he added.

An example solution is NXP’s A5M36TG140 fully integrated Doherty PA module designed for wireless-infrastructure applications like mMIMO systems, outdoor small cells and low-power remote radio heads. The LDMOS and GaN-on-SiC PAs are designed for TDD LTE and 5G systems.

Enhanced MIMO performance also brings system design challenges like the size and weight of the radios. This has resulted in increasing demand for smaller and more efficient PAs.

“In addition to the traditional RF parameters of gain, bandwidth and efficiency, solutions are being offered to reduce the size and weight of radios,” Westberg said.

One example is NXP’s recently introduced thermal solution, called top-side cooling, for RF power modules, which enables smaller, thinner and lighter radios for 5G base stations. NXP said it will reduce the thickness and weight of 5G radios by more than 20%.

“This solves several system design challenges by simplifying the thermal design of a radio,” Westberg said. “It will take traditional and innovative solutions like this to meet the increased requirements of mMIMO systems.”

Typical mMIMO units have either 32T32R or 64T64R channel configurations, Forbes said. “In 5G Advanced, we expect to see up to 128T128R or even higher. This places pressure on the integration level and size of all of the components in the unit.”

Analog Devices recently introduced its ADRV9040 RadioVerse transceiver system-on-chip, which integrates 8T8R channels along with the digital front end (DFE), including DPD, crest factor reduction and channel digital up-/down-conversion.

Forbes said this device enables customers to build lower-energy, smaller and lighter mMIMO radio units.

Another system-level challenge is higher frequencies.

“With higher-frequency operation, the path losses increase, so the antenna array element count increases to increase the antenna gain to overcome the loss and maintain coverage,” Gengler said.

With the higher number of antenna array elements, the PA in each channel will have lower power requirements, and it also increases the need for a corresponding DFE for each channel, which increases the radio bill of materials, he explained.

This will require system-level optimization of the RFFE, DFE and DPD, Gengler said. “Higher-frequency operation of a PA inherently reduces efficiency, so efficiency improvements from device technology and circuit design will be important to keep the radio heatsink as small as possible.”

Role of WBG semiconductors

GaN technology, with its advantages over traditional silicon-based counterparts, including higher switching frequencies, higher voltages and lower losses, is finding more homes in 5G networks. This is becoming increasingly important in 5G as the number of RF devices needed for the antennas continues to rise while maintaining the same size and reducing power consumption.

There is agreement in the industry that GaN will play a vital role in solving some of the challenges around RF and power design in 5G networks.

Gengler expects compound semiconductors like gallium arsenide (GaAs) and GaN to meet the new frequency and bandwidth requirements of 5G.

“At the core of many of the current and next-generation solutions for 5G Advanced is semiconductor technology,” Westberg said. “GaN offers improved efficiency and increased bandwidth in a small footprint when compared with other technologies.

“Best performance can be achieved with a GaN technology that is designed for cellular-infrastructure applications,” he added. “That is why it is fast becoming the technology of choice for higher-power applications for cellular infrastructure.

“GaN can withstand high electrical fields, which allow the devices to be operated at high voltage,” Gengler said. “The devices have high charge mobility and high power density, which reduces parasitic capacitance, allowing for high frequency and wider bandwidth operation.

“The high power density of GaN devices translates to smaller devices than competing technologies to realize a given power level, which leads to higher efficiency and higher inherent device impedances,” he added. “The higher intrinsic device impedances and lower parasitic capacitance of the devices enable wider-bandwidth–matching networks to realize the widest bandwidths.”

LDMOS was the technology of choice for many years, said Forbes. “As cellular networks have moved to higher frequencies—for example, 3.5 GHz and beyond—and wider bandwidths—for example, 200 MHz—GaN tends to be more efficient and allows higher temperature of operation, simplifying cooling.

“Higher frequencies will inevitably be a part of 5G Advanced and 6G,” he added.

The topic of 4.9-GHz, 6-GHz and 7-GHz bands for mobile use will be debated at the World Radio Conference 2023, Forbes said. “At these frequencies, GaN devices hold a lot of promise.”

However, GaN also poses some challenges. One example is a phenomenon called charge trapping, which “introduces a new, more complex non-linearity in the amplifier relative to LDMOS, and the digital pre-distortion algorithm must be capable of addressing this,” Forbes said.