A lurking threat behind the promise of 5G delivering up to 1,000 times as much data as today’s networks is that 5G could also consume up to 1,000 times as much energy. Concerns over energy efficiency are beginning to show up at conferences about 5G deployments, where methods for reducing energy consumption have become a hot topic.
The International Telecommunication Union (ITU) has published challenging, measurable requirements on the data rates, latency, and reliability that a network needs to satisfy to be called 5G. While the ITU has also aimed for greater energy efficiency, it hasn’t established any measurable goals for it.
Emil Björnson, an associate professor at Linköping University, in Sweden, has devoted a portion of his current research to addressing this issue. Despite the challenges, he remains optimistic. “This is a major problem, but I don’t think it will be a showstopper,” said Björnson.
Björnson says this despite concern about two elements expected to be fundamental parts of 5G networks: an increase in the number of small cells and the rise of massive multiple-input multiple-output (MIMO) antennas.
In the case of small cells, the Small Cell Forum predicts that 5G small-cell deployments will overtake 4G small cells by 2024, with the total installed base of 5G or multimode small cells in 2025 to be 13.1 million, constituting more than one-third of the total small cells in use.
Björnson concedes that when you deploy more small cells, the total energy consumption of a network will grow. However, he notes that energy consumption in a small cell is much lower than in a conventional cell. But, many more small cells will be needed to cover an area. That makes it hard to predict how large their net energy consumption will be.
When it comes to massive MIMO, the technology involves the use of arrays with many more antennas at each base station. As a result, there are many more hardware components per base station. Björnson believes this will probably increase the total energy consumption of 5G base stations compared to 4G. But as massive MIMO technology develops, its energy efficiency may also improve over time.
“Just as computer processors become vastly more efficient over time, the analog and digital circuits that are used in base stations become more efficient,” said Björnson. “The first generations of 5G hardware will be all about delivering all the new features to the market, but then there will be time to refine the hardware, as well.”
As evidence that this will be a likely outcome, a European Union project dubbed the MAMMOET project has predicted that future massive MIMO base stations will consume less energy than 4G base stations, despite the fact that they will contain more hardware.
The upside of the refinements to massive MIMO hardware over time will be that this equipment can serve many more users at the same time and frequency. This capability is called spatial multiplexing and because of it, energy consumption is divvied up between users. “If you spatially multiplex 10 users and need to spend twice the energy to do that, you will still be five times more energy efficient,” said Björnson.
In both 4G and future 5G networks, operators will probably run their base stations so they transmit at the maximum power allowed by their licenses, in order to maximize the coverage, according to Björnson. As a result, no direct savings are expected to be found in transmission when comparing 4G and 5G base stations that are deployed in similar places (on rooftops and masts) and using typical cellular frequencies between 1 and 5 gigahertz.
However, there is one particular feature that will make 5G networks less energy demanding: the base stations in 5G can be put into a “sleep mode” (referred to as "ultra-lean design”) whenever there are no active users.
“This happens much more frequently than one might think,” said Björnson. “4G networks need to transmit a lot of control signals even when no one is listening—for example, at night.”
According to recent research, the ultra-lean design that 5G networks are capable of will make it possible to put more components to sleep for a longer time, reducing energy consumption by almost 10 times compared to current systems when there are no users.
Once you look outside the specific technologies related to 5G networks, like massive MIMO, there is a general issue that even if a new technology is more energy efficient, or consumes less energy, it will take time before it becomes popular enough to provide noticeable differences across a network, according to Björnson. But he believes the ongoing shift toward software-defined network equipment could change that. He added: “If new features that make the system increasingly more energy efficient can be delivered as software updates, it will be much easier to improve the efficiency over time.”