5G New Radio (NR) is fundamentally different from its 4G predecessor and not just a simple grade from existing 4G infrastructure. The use of multi-user massive-MIMO, integrated access and backhaul, and beamforming with millimeter-wave (mmWave) spectrum up to 71 GHz gives 5G NR the ability to provide huge levels of connectivity, speeds in the multi-gigabit range, and latencies of about a millisecond.
Unsurprisingly, the market for 5G NR is expected to see very rapid growth as users demand access to this latest technology. Research firm ResearchAndMarkets estimates1 that the 5G infrastructure market will grow annually, at a compound annual growth rate of 55% from 2021 to 2026, to reach a market size of $115.4 billion.
Behind this growth is the requirement for very large numbers of small cells to deliver the line-of-sight coverage necessary for the higher frequencies employed by 5G NR, requiring a change to the cell station architecture and a reduction in overall size and weight. Cells will be found in many places, including on street lighting and buildings — almost anywhere there is height and available power. And power is one of the key challenges for 5G. Currently, according to MTN Consulting,2 4G electricity represents about 5% to 6% of a mobile operator’s operating. 5G NR will need at least twice the power of 4G and, factoring in current increases in energy costs, opex costs are set to rise significantly.
Small cells for 5G
The 5G power challenge
Among the difference between 5G and previous technologies (2G, 3G, and 4G) is the internal base station architecture. In earlier systems, the power amplifier (PA) and power supply unit (PSU) were entirely separate with their own thermal management, typically a heatsink. With 5G NR, it is likely that the PSU will be integrated into the gNodeB, along with the remote radio unit (RRU) to form an active antenna unit (AAU) — which would have a single heatsink.
Difference between 5G and earlier-generation internal base station architecture (Source: IEEE)
The architecture change brings more challenges for power design, which, when combined with issues such as confined space, elevated temperatures, sealed environment, and the need for lightweight solutions, adds even more complexity to designing AC/DC power solutions for 5G. This is further exacerbated by the fact that PAs are typically less efficient than PSUs, which raises the temperature of the now-shared heatsink, raising the operating temperature for the PSU from ~85˚C to close to 100˚C. This increased temperature has the potential to impact reliability, as heat is a key contributor to component failures.
Based on the rule of thumb that MTBF for a PSU halves for every 10˚C rise in component temperature, it can be seen that the integration could reduce PSU lifetime by between 50% and 75%. This is important, as mobile operators are seeking PSU lifetimes in the range of seven to 10 years, due to the huge number that will be deployed as well as the difficulty and cost in access and replacement.
Signal integrity is a fundamental requirement of any radio-based system such as 5G. However, integrating the PSU and RRU to create an AAU increases the possibility of signal interference, which would degrade system performance. The interference issue is two-fold. First, switching PSUs generate electromagnetic interference (EMI), and these must be constrained within tight limits to ensure that they do not interfere with the PA and/or RRU. The PSU must also be sufficiently shielded so that the 5G radio signals do not interfere with its operation.
Passive intermodulation is a concern when multiple signals pass through junctions formed from dissimilar materials — including loose cable connections, contaminated surfaces, poor performance duplexers, or aged antennas — and mix to produce sum and difference signals within the same band, thereby causing interference. This must be considered during all aspects of the design to ensure it does not become an issue.
Addressing the power challenges
Various approaches have been undertaken to reduce the power consumption of 5G NR cells. One approach involved replacing the 64T64R MIMO antennae with less power-hungry 8T8R or 32T32R antennae. While this does reduce power consumption, there are performance tradeoffs — and the additional PAs actually increase power needs in many cases.
Heatsinking of PSUs will be required in 5G applications.
Pulsed power is seen by many as a potential solution. As a 5G base station is able to analyze traffic loads, it can enter “sleep mode” when traffic is light. This is a significant advantage over 4G, which is “always on,” constantly transmitting reference signals to detect users. However, even in sleep mode, essential functions must remain in operation — not least to permit emergency (911) calls as well as ensure that time-sensitive internet-of-things traffic is not interrupted.
Underlying semiconductor technology has an important role to play when it comes to addressing some of the challenges. Indeed, the semiconductor industry is undergoing a fundamental change to address the rapidly changing needs of a number of applications, including automotive, renewable energy, and 5G. These applications demand even higher levels of performance, efficiency, and reliability in harsh environments and at elevated temperatures.
For decades, silicon has been the mainstay of semiconductor devices. However, this is being replaced in the most challenging applications by new wide-bandgap (WBG) materials, including silicon carbide and gallium nitride. Higher electron mobility brings a number of benefits that are significant in the context of challenging power applications.
Benefits of WBG devices in applications requiring high performance and high efficiency
With WBG devices, static and switching losses are lower compared with equivalent Si devices. This increases efficiency and allows for operation at higher frequencies, which, in turn, allows passive components to be smaller and more cost-effective. This also helps to reduce weight, a critical consideration for 5G mmWave antennas, as these often need to placed on masts to achieve the height necessary to clear obstacles. If the antenna weight can be kept down, then mast design and deployment is simpler, more flexible, and cheaper.
In addition, WBG devices can operate at elevated temperatures, which increases reliability. Finally, SiC and GaN also tend to produce less EMI, which means that less filtering and shielding is required — a very useful benefit in 5G systems.
5G represents a significant change from previous cellular technologies, with higher frequencies leading to closer placement of base stations and the deployment of many more cells. While these changes will deliver a robust, high-performance communications solution with greater throughput and lower latencies than ever before, they also bring significant challenges — especially for power. Depending on the cell and specific design requirements, AC/DC power requirements for 5G RAN deployments can range from just a few hundred watts to many kilowatts.
The PSUs used in lower-power applications are typically embedded within the antenna unit and rely on the antenna for the cooling heatsink and sealed enclosure for IP protection. For higher-power applications — for example, powering the baseband unit, powering the radio units, and charging the site battery backup unit — higher-power outdoor-rated PSUs are often used, each self-contained within their own IP65-rated enclosures. These PSUs, which can be paralleled to provide even higher output power, help users to configure compact bulk power systems that provide the very high output capabilities that are demanded by many 5G applications.
Maximizing efficiency is important to control the operating costs of a network that will consume at least twice as much energy as its predecessors as well as ensure reliable operation despite higher temperatures and minimum opportunities for cooling. Fundamental architecture modification may help to address the power challenge, but changing structures increase the potential for interference that would degrade network performance.
The solution lies in intelligent operation through pulsed power and the implementation of new semiconductor technologies including WBG that allow for the development of even more rugged, efficient, and compact power technologies.
As a leading provider of high-efficiency, high-density, rugged power solutions designed for outdoor and harsh-environment operations, Advanced Energy recognizes the role that power supplies play in 5G infrastructure buildout. The company is conducting research on ways to operate at higher heatsink temperatures without affecting product life, ways to reduce power consumption when in standby mode in pulse-power operation, and ways to utilize WBG devices to shrink the PSU so it can be more easily integrated into the AAU.
References
1Global 5G Infrastructure Market Report 2021: Market Is Expected to Grow From $12.9 Billion in 2021 to $115.4 Billion by 2026 – ResearchAndMarkets.com. (2021, September 10). Business Wire. bwnews.pr/3xaHKJU
2M. Walker. (2020, March 27). “Operators facing power cost crunch.” MTN Consulting. bit.ly/3tqciGt
This article was originally published on EEWeb.
Dib Nath is the senior director of marketing for telecom at Advanced Energy.