Rakuten likes to be thought of as the open RAN frontrunner, a nimble challenger showing its elderly rivals what the new technology can do.

But the narrative has a few holes. Rakuten's mobile rollout in Japan is costing more than it seemed to anticipate. The relatively lukewarm consumer response has disappointed parts of the investor community. And those elderly Japanese rivals do not look so decrepit.

In fact, a sensible argument could be made that NTT DoCoMo and not Rakuten is the real poster boy for open RAN. Japan's biggest telco already claims to have built an extensive 5G network based on open RAN fundamentals. In short, that means using one supplier for radios and another for baseband – instead of the traditional, buy-everything-from-the-same-vendor approach.

"Our RAN is fully multivendor interoperable – that means even in the same geographic area we use different vendors' equipment for CU/DU [central unit/distributed unit] side and RU [radio unit] side," said Sadayuki Abeta, the general manager of NTT DoCoMo's RAN development department, during Light Reading's Open RAN Digital Symposium this week.

"This multivendor network we deployed from day one and now more than 10,000 basestations we deployed," continued Abeta. He is targeting 20,000 by next March.

Earlier commentary points to Nokia as one of the baseband suppliers and Japan's own Fujitsu as a provider of radio units. Despite this, Nokia has recently been criticized by European operators for not walking the walk.

"Nokia has developed open RAN software functions, but these only run on Nokia proprietary hardware," said Deutsche Telekom, Orange, Telecom Italia, Telefónica and Vodafone in a report aimed at European authorities.

Separately, Nokia also supplies 4G radios to Rakuten, which is using them with baseband software from its own Altiostar unit. The Finnish vendor declined to comment on its role in the NTT DoCoMo network.

Abeta says there are two radio unit vendors in commercial deployment and that another two have been certified. A 5G deal with South Korea's Samsung was announced in March, although few details were provided about Samsung's role at the time.

Earlier today, NTT DoCoMo flagged successful trials of a 5G standalone baseband unit from NEC, another Japanese vendor. NEC's technology conforms to O-RAN specifications, noted the operator.

Rakuten the also RAN

NTT DoCoMo's efforts seem to place it far ahead of Rakuten on both 5G and open RAN deployment. During its last earnings update, Rakuten claimed to have 30,000 basestations in operation, but the vast bulk seem to be 4G ones.

By March, it had deployed only 1,000 5G basestations and there has been no clear update on progress or targets since then. What's more, the 4G rollout is not compliant with the specifications drawn up by the O-RAN Alliance, Rakuten has acknowledged.

NTT DoCoMo's 5G deployment, by contrast, uses the O-RAN fronthaul interface between the baseband unit and the radio, says the operator. It also takes advantage of carrier aggregation, an advanced feature that combines spectrum from different frequency bands to boost performance. Speeds of up to 4.2 Gbit/s are achievable, says Abeta.

So far, NTT DoCoMo has been able to convert 5.35 million of its roughly 82 million customers to 5G services. That compares with the 5.1 million that Rakuten serves altogether, including about 1 million customers at its mobile virtual network operator (MVNO) business (MVNOs rely on wholesale agreements with network owners).

Want to know more about 5G? Check out our dedicated 5G content channel here on Light Reading.

Abeta's company has launched an open RAN partnership program to speed up development and tackle some of the main challenges. One concern is whether total cost of ownership will be lower – the need for integration and interoperability testing represents an additional cost for operators, says Abeta.

Another issue is the poor performance of the common, off-the-shelf equipment that virtualization brings. NTT DoCoMo reckons this can be improved with hardware accelerators, specialized silicon that major chipmakers are developing.

The operator's open RAN partners now include four major silicon suppliers – Intel, Nvidia, Qualcomm and Xilinx – as well as Dell, Fujitsu, HPE (which joined in October), Mavenir, NEC, NTT Data (a sister company), Red Hat, VMware and Wind River.

Gabriel Brown, a principal analyst with Heavy Reading (a Light Reading sister company) points out that NTT DoCoMo has been running multivendor networks for many years, having previously mixed baseband and radio suppliers in its 4G network. Given the activities of Rakuten and other Japanese operators, the Asian country is now clearly in the vanguard.

"You can make a strong case that Japan is the most technically advanced open RAN market," says Brown.

Update: This story has been amended since it was first published to include a longer quote from Sadayuki Abeta.

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— Iain Morris, International Editor, Light Reading