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The wireless industry is divided on Open RAN’s goal to make network components interoperable
We've all been told that 5G wireless is going to deliver amazing capabilities and services. But it won't come cheap. When all is said and done, 5G will cost almost US $1 trillion to deploy over the next half decade. That enormous expense will be borne mostly by network operators, companies like AT&T, China Mobile, Deutsche Telekom, Vodafone, and dozens more around the world that provide cellular service to their customers. Facing such an immense cost, these operators asked a very reasonable question: How can we make this cheaper and more flexible?
Their answer: Make it possible to mix and match network components from different companies, with the goal of fostering more competition and driving down prices. At the same time, they sparked a schism within the industry over how wireless networks should be built. Their opponents—and sometimes begrudging partners—are the handful of telecom-equipment vendors capable of providing the hardware the network operators have been buying and deploying for years.
These vendors initially opposed the scheme, called Open RAN, because they believed that if implemented, it would damage—if not destroy—their existing business model. But faced with the collective power of the operators clamoring for a new way to build wireless networks, these vendors have been left with few options, none of them very appealing. Some have responded by trying to set the terms for how Open RAN will be developed, while others continue to drag their feet, and risk being left behind.
The technology underpinning a generation of wireless like 5G can take a decade or more to go from initial ideas to fully realized hardware. By comparison, Open RAN has emerged practically overnight. In scarcely three years, the idea has gone from little more than a concept to multiple, major deployments around the world. Its supporters believe it will nurture immense innovation and lower the costs of wireless access. Its detractors say it will threaten basic network security and could lead to disaster. Either way, this is a watershed moment in the communications industry, and there's no turning back.
Rakuten Mobile's Open RAN network includes 4G radios from Nokia running software from another vendor. The company has deployed one such RAN at the company's global headquarters in Tokyo. The Open RAN network also uses servers to power the cloud-native network. Photos: Rakuten
Broadly speaking, a radio access network (RAN) is the framework that links an end device like a cellphone and the larger, wired, core network. A cellular base station, or tower, is the most familiar example of a RAN. Other varieties of base stations, such as the small cells that send and receive signals over short distances in 5G networks, also fit the bill.
To function as this link, the RAN performs several steps. When you use your phone to call a friend or family member in a different city, for example, you need to be within range of a cell tower. So the first step is for the cell tower's antennas to receive the phone's signal. Second, a radio converts the signal from analog to digital. Third, a component called the baseband unit processes the signal, corrects errors, and finally transmits it into the core network. Within the RAN, these components—the antenna, the radio, and the baseband unit—can be, and often are, treated as discrete chunks of technology.
If you separate the radio and the baseband unit from one another, and develop and construct them independently, you still need to make sure that they work together. In other words, you need their interfaces to be compatible. Without such compatibility, data can be garbled or lost when moving from the radio to the baseband unit, or vice versa. In the worst-case scenario, a radio and a baseband unit with incompatible interfaces will just not work together at all. A functional RAN needs to have a common interface between these two components. However, astonishingly, there is currently no guarantee that a radio manufactured by one vendor will be interoperable with a baseband unit manufactured by another vendor.
The specifications for RAN interface standards, like all of those for cellular networks, are set by the 3rd Generation Partnership Project. Gino Masini, the chair of 3GPP's RAN3 working group, says that many of 3GPP's specifications, including those covering interfaces, are designed with interoperability in mind. However, Masini, who is also principal researcher for standardization at Ericsson, adds that there is nothing preventing a vendor from “complementing" a standardized interface with additional proprietary techniques. Many vendors do just that—and Masini says this does not limit vendor interoperability.
Others in the industry don't agree. “Both Nokia and Ericsson are using 3GPP interfaces that are supposed to be standard," says Eugina Jordan, the vice president of marketing at Parallel Wireless, a New Hampshire–based company developing Open RAN technologies. But “those interfaces are not open, because each vendor creates their own flavor," she adds. Most of these vendor-specific tweaks occur in the software and programming languages used to connect the radio to the baseband unit. Jordan says that the tweaks primarily take the form of vendors defining radio parameters that were intentionally left blank in 3GPP standards for future development.
Ultimately, this leads to each vendor constructing hardware that is too incompatible with the others' for operators' comfort. “We see with 3GPP specification more and more gaps," says Olivier Simon, the radio innovation director at Orange, an operator based in France. Simon says that of the interfaces specified by 3GPP, “you can see that many of them are not really open in the sense that they are not enabling multivendor cooperation on both sides of the interface."
The O-RAN Alliance, of which Simon is an executive committee member, is the largest industry group working on Open RAN specifications. The group formed in 2018, when five operators—AT&T, China Mobile, Deutsche Telekom, NTT Docomo, and Orange—joined to spearhead more industry development of Open RAN. “I think the realization was, we need to create one unified, global operator voice to drive this disaggregation and openness," says Sachin Katti, an associate professor at Stanford University and one of the cochairs of the O-RAN Alliance's technical steering committee.
O-RAN Alliance members hope Open RAN can plug the gaps created by 3GPP's specifications. They're quick to say they're not trying to replace the 3GPP specifications. Instead, they see Open RAN as a necessary tightening of the specifications to prevent big vendors from tacking their proprietary techniques onto the interfaces, thereby locking wireless operators into single-vendor networks. By forcing open interfaces, the wireless industry can arrive at an entirely new way to engineer its networks. And if those open interfaces promote more competition and lower prices, so much the better.
As early 5G deployments were underway around the world, in 2019, the wireless industry group GSM Association predicted that operators would spend $1.3 trillion on 5G infrastructure, equipment, and technologies for their networks. RAN construction will consume the lion's share of those capital expenditures. And much of that spending will go toward the handful of vendors that can still provide complete end-to-end networks.
“This was always the pain point, because RAN is the most expensive part of an operator's deployment," says Sridhar Rajagopal, the vice president of technology and strategy at Mavenir, a Texas-based company that provides end-to-end network software. “It takes almost 60, 70 percent of the deployment costs." By 2025, the GSM Association predicts, operators will be spending as much as 86 percent of their capital budgets on RAN.
Inside the Radio Access Network
Cellular networks send signals over long distances using a wired or fiber-optic backbone called a core network. The radio access network (RAN) functions as a middleman, connecting an end device like a cellphone to the core network by receiving the phone's wireless signal with its antenna, converting the signal to digital in the radio unit, and performing tasks like data processing and error correction in the baseband unit. In current 5G systems, the baseband unit splits those tasks between a distributed unit and a centralized unit. Open RAN concepts hope to build on that split to create more flexible, thinly sliced RANs.
Not surprisingly, with so much money on the line, operators do everything they can to avoid any fiascoes caused by incompatible hardware. The surest way to avoid such a disaster is to stick with the same vendor from one end of the network to the other, thus avoiding any possibility of mismatched interfaces.
Another factor contributing to operator unease is the dwindling number of companies that can provide cutting-edge end-to-end networks. It's now just three: Ericsson, Nokia, and Huawei. This trio of end-to-end vendors can charge high prices because operators are essentially locked into their systems.
Even the arrival of a new generation of wireless doesn't create a clear opportunity for an operator to switch vendors. New wireless generations maintain backward compatibility, so that, for example, a 5G phone can operate on a 4G network when it's not within range of any 5G cells. So as operators build out their 5G deployments, they're mostly sticking with a single vendor's proprietary tech to ensure a smooth transition. The main alternative is scrapping everything and paying even more for a new deployment from the ground up.
There is broad consensus in the wireless industry that Open RAN is making it possible to pick and choose different RAN components from different vendors. This opportunity, called disaggregation, will also remove the stress over whether components will cooperate when plugged together. Whether or not disaggregation is a good thing depends on whom you ask.
Operators sure like it. Dish, a television and wireless provider, has been particularly aggressive in embracing Open RAN. Siddhartha Chenumolu, vice president of technology development at Dish, describes his first reaction to the technology: “Hey, there might be something here where it allows us to disaggregate completely," he says. “I don't have to rely on Ericsson only to provide radios, or Nokia only." Dish has committed to using Open RAN for a ground-up deployment of a 5G network in the United States this year.
Proposed Open RAN Functional Splits
Proponents of Open RAN are exploring several possible “functional splits" to create new, interoperable interfaces in RAN systems, with four possibilities gaining the most traction. Each split assigns the many tasks a RAN undertakes to create a link between the core network and an end device in different ways, based on what different kinds of cellular networks might need. Split 2, for example, creates highly intelligent radio units that handle much of the data processing before the signal is ever transferred. On the other hand, Splits 7.2x and 8 create “dumb" radios that minimize data processing in favor of lower latencies.
Smaller-scale and more specialized vendors are also optimistic about the boost Open RAN can bring to their businesses. For Software Radio Systems, a maker of advanced software-defined radios, Open RAN makes it easier to focus on developing new software without worrying about losing potential customers intimidated by the task of integrating the tech into their wider networks.
Not surprisingly, the big three remaining hardware vendors take different views. In February, Franck Bouétard, the CEO of Ericsson France, called Open RAN an “experimental technology" that was still years away from maturity and could not compete with Ericsson's products. (Ericsson declined to comment for this article).
But some in the industry see the hardware makers as deliberately slowing down the development of Open RAN. “Some of the big vendors, they're continuously raising one issue or another," says Paul Sutton, a director at Software Radio Systems. “Ericsson is probably in the party that's fighting back the most against Open RAN, because they will probably have the most to lose."
Not every big vendor is pushing back. Nokia, for example, sees opportunity. “I think we need to accept the fact that Open RAN is going to happen anyway, with or without us," says Thomas Barnett, a mobile-network strategy and technology lead at Nokia. “We, at Nokia, decided to be proactive in taking a leadership position in order to grab a better market-share position." Japanese operator Rakuten's Open RAN deployments are using Nokia's equipment, for example, and Nokia is also working with Deutsche Telekom to deploy an Open RAN system in Neubrandenburg, Germany, later this year.
That's not to say Nokia or other vendors are on the same page as the operators and the specialized vendors like Software Radio Systems. At the moment, there's still plenty of debate. Ericsson and other vendors argue that creating more open interfaces will inevitably create more points in the network for cyberattacks. Operators and other Open RAN proponents counter that standardized interfaces will make it easier for the industry to identify and fix vulnerabilities. Everyone seems to have a different opinion on how much openness is enough openness, or on just how much the RAN hardware elements should be disaggregated.
In its most ambitious version, Open RAN would split the RAN into smaller components beyond the radio and the baseband unit. Proponents of this level of disaggregation believe it would bring even more vendors into the wireless industry, by allowing companies to hyperspecialize. An operator could contract with a vendor for just the processor that readies the data received from the core network for wireless transmission, for example. Many in the industry also say that this kind of specialization would speed technological innovation by making it possible to swap out and deploy a new RAN component without waiting for the entire radio or baseband unit to be upgraded. “That's maybe one of the brightest opportunities that Open RAN could provide," says Ted Rappaport, the founding director of NYU Wireless, a research center for advanced wireless technologies.
The wireless industry's first efforts with disaggregation were inspired by 5G specifications themselves. These specifications split the baseband unit, which is responsible for processing and transferring data to or from the core network, into two smaller components. One component is the distributed unit, which takes over the data-processing responsibilities. The other component is the centralized unit, which handles the connection to the core network. The advantage of splitting the baseband unit in this way is that the centralized unit no longer needs to be located at the cell tower itself. Instead, a single centralized unit can sit in a local server farm, maintaining the connection to the core network for multiple cell towers in the area.
The O-RAN Alliance is working on a handful of different “functional splits" in the RAN to create more opportunities for disaggregation beyond this split between the distributed unit and the centralized unit. Each of these additional splits creates a division somewhere amid the many steps between a signal's arrival from the core network and its transmission to a cellphone. It's a bit like taking a lunch break: You can take an early lunch and thus shift many of your responsibilities to the afternoon, or work for several hours before opting for a later lunch.
One important split, called Split 7.2x, hands responsibilities such as signal encoding and decoding, as well as modulation, to the distributed unit. On the other side of the split, the radio is responsible for some light processing duties like beamforming, which establishes the specific direction of a transmission. The radio is also still responsible for converting digital signals to analog signals and vice versa.
Another split, Split 8, shifts even the responsibility for beamforming to the distributed unit, leaving the radio responsible only for converting signals. In contrast, Split 2 would push encoding, decoding, modulation, beamforming, and even more processing responsibilities to the radio, leaving the distributed unit responsible only for compressing data to a smaller number of bits before transferring the data to the centralized unit.
The goal in creating open standards for multiple kinds of splits is that operators can then purchase better-tailored components for the specific kind of network they're building. For example, an operator might opt for Split 8 for a large-scale deployment requiring a lot of radios. This split allows the radios to be as “dumb," and therefore cheap, as possible because all of the processing happens in the centralized unit.
It's technically possible to put together a disaggregated RAN with open interfaces using only hardware, but defining the components in software has some advantages. “Our industry has become really, really hardware-centric," says Chih-Lin I, who, along with Stanford's Katti, is cochair of the O-RAN Alliance's technical steering committee. “Every generation of our networks basically rely on special-purpose hardware with tightly coupled software. So every time we need to have an upgrade, or new release, or new fractional release, it takes years."
In order to move away from a hardware-centric attitude, the O-RAN Alliance is also encouraging the wireless industry to incorporate more software into the RAN. Software-defined networks, which replace traditional hardware components with programmable software equivalents, are more flexible. Upgrading a virtual component can be as simple as pushing out new code to the base station.
The emphasis on software is also making it possible for the industry to consider entirely new technologies, the most important of which is the RAN Intelligent Controller. The RIC collects data from the RAN components of dozens or hundreds of base stations at once and uses machine-learning techniques to reconfigure network operations in real time. It bases the modifications on whether particular cell towers are under a heavy traffic load, for example, or transmitting in a heavy rainstorm that might dampen signals. The RIC can reprogram the RAN's software components in order to deliver better service. “Imagine the possibility where I can really adapt my network, based on the user experience, how the user is feeling in real time," says Dish's Chenumolu. “How great is that?"
Since its founding in 2018, the O-RAN Alliance has ballooned from its five founding members—all operators—to more than 260 members. Of the big three vendors, only Huawei is not a member, citing its belief that Open RAN systems cannot perform as well as the company's proprietary systems. Other Open RAN groups are growing at a similar pace. The Open RAN Policy Coalition, for example, was founded in May 2020 and already has over 60 members working to coordinate global policy on Open RAN development and deployment.
Rakuten's engineers can install a 4G base station for its Open RAN deployment in as little as 8 minutes.
In recent months, Rakuten Mobile, a unit of the Japanese e-commerce giant, and Dish have committed to Open RAN for extensive new 5G deployments. After a mandate from the British government to strip all Huawei components from wireless networks, England-based Vodafone is replacing those components in its own networks with Open RAN equivalents. Because of similar mandates, local operators in the United States, such as Idaho-based Inland Cellular, are doing the same.
These deployments haven't always gone as planned. Rakuten, in particular, faced some initial setbacks when its Open RAN network's performance didn't match the performance of a traditional end-to-end system. The operator remains optimistic, however, and hasn't given up on it. Many in the industry aren't concerned about these kinds of issues, arguing that the only way to actually iron out the wrinkles in the technology is to deploy it at scale and see what works and what needs improvement.
There are also still lingering questions over where the buck stops. When an operator buys an end-to-end system from Nokia or Ericsson or Huawei, it also knows it can depend on that vendor to support the network when problems crop up. Not so with Open RAN deployments, where no single vendor is likely to claim responsibility for interoperability issues. Larger operators will likely be able to support their own Open RAN networks, but smaller operators may be reliant on companies like Mavenir, which have positioned themselves as system integrators. Critics, however, see that approach as just creating another kind of end-to-end vendor—and adding additional expense—for operators that don't have the expertise or resources to support their own networks.
In the end, Open RAN's true test may come when it's time to implement the next generation of wireless. “I think 6G will be built with Open RAN as a prior assumption," says Rajat Prakash, the principal engineer of wireless R&D at Qualcomm.
It remains to be seen how far the movement will go to disaggregate the RAN, to open up new interfaces, or even to bring new technologies into the mix. What's important is that the movement has already gained substantial momentum. Even though some corners of the industry still have reservations, operators and small-scale vendors have put too much weight behind the idea for the movement to fizzle out. Open RAN is here to stay. As it matures, the wireless industry will be open for a new way of doing business.
This article appears in the May 2021 print issue as “The Clash Over 5G's First Mile."