Nokia lays down 5G LTE multi vendor fix

No Huawei 5G, no problem? Nokia proposes overlay solution to enable multi-vendor 4G-5G radio access networks.

Nokia’s radio unit has outlined a solution to the thorny issue of deploying a 5G NR Radio Access Network (RAN) from one vendor on top of an existing LTE network from another.

nokia 5G NR LTE overlayYou can read the full blogpost here, but what follows is Nokia’s proposal in essence. 5G NSA (Non StandAlone mode) requires an LTE anchor. To interface between a 5G NR radio layer and the LTE layer requires inter-vendor X2 integration. That’s not easy because even though X2 is a standardised interface, vendors tend to implement it in different ways. (Note, this final point is TMN’s extrapolation, not Nokia’s. But clearly if it was a trivial thing to do we wouldn’t be having this discussion in the first place. Vodafone UK CTO Scott Petty, for example, was recently reported as saying, “You can’t run one 5G vendor attached to another 4G vendor.)

However, the post explains that if you deploy a new, lower band, LTE radio from Nokia at the same time as you deploy the higher band 5G NR radio, then you can use the new LTE radio as your NSA anchor and the inter-working between the two is easy-as. The post states: “Nokia has a simpler alternative solution that does not require X2 interworking between an incumbent and new vendor but facilitates a ‘new’ Nokia overlay with minimal support from an incumbent vendor.”

Further, when you move to 5G NR SA (Standalone) and no longer need the LTE anchor for control, then you can migrate towards using that lower band spectrum as a coverage band for 5G NR SA by using dynamic spectrum sharing.

So, how would this work – and would the overlay approach mean that operators have to clear some existing LTE spectrum to make room for the new carrier: if so, how much? We asked blog author Harri Holma, for some more details. Here’s his response:
To make this happen, Nokia LTE needs to take some spectrum, typically 5-10 MHz. Operators may have a new block of spectrum where this additional amount can be taken from, like the new 700 MHz allocation which is unused in many markets today. Another option is at 2100 MHz which is still partly used by 3G and could be re-farmed to LTE/5G while moving 3G to 900 MHz. 

“The additional capacity opened by adding new 5G spectrum, and the migration of users’ data traffic to that, means that the overall network capacity can be substantially increased even if a small amount of LTE capacity is used in this way by the Nokia overlay.”

We also asked what the cost implications of the overlay model were. What difference has Nokia modelled in terms of cost and time to deployment for the overlay approach versus inter-vendor integration?

“An additional LTE RF unit is needed in the first phase but a low band RF unit is needed anyway for 5G with standalone (SA) architecture. Nokia’s multi-band antennas mean that this additional LTE layer can be added in the same tower-climb as would be required anyway when adding new 5G spectrum to the network. Therefore, we are saying that there are no additional investments needed for the LTE anchor because a similar RF investment is anyway needed for 5G SA.”

Chinese off the menu?

Although the blog post doesn’t mention it specifically, there’s one very current aspect to this: namely that some European operators that have Huawei LTE networks have claimed that if they are banned from having Huawei 5G RAN they may face long delays in deploying 5G. This is because either they will have to go through extensive engineering to get the Huawei LTE RAN to interconnect with the new 5G layer or, in an even more extreme case, because they will have to rip and replace the 4G layer and replace it with one that can play with the 5G vendor.

We asked blog author Harri Holma, a Nokia Bell Labs fellow, if this overlay solution is in effect a “no Huawei, no problem” solution, and he said not really – the solution of course can be deployed over any legacy 4G RAN, meaning it is not specifically focussed at operators with Chinese vendor RAN. Here’s his answer:
“The solution is designed as a simple and streamlined way to deploy non-standalone Nokia 5G NR on top of ANY vendor LTE network. So now it need not be true that if you have a 4G radio from vendor, you must have 5G NR from the same vendor.”

Of course Holma is correct. If it works, it works, and therefore the solution is equally an answer to an operator that has, say, an Ericsson or Samsung LTE RAN, and wants to change vendor for 5G. However, Nokia’s own marketing supremo Barry French, CMO, perhaps said out loud what many are thinking when he tweeted: “This should help address operator concerns if they want to address issues raised by governments about their current vendors.” There’s only really one way to interpret that, unless you know of governments raising issues about anyone other than Huawei or ZTE.

You’d also have to say that if this architecture helps Nokia win business on top of rival vendors’ LTE networks, then the reverse could be true too, as long as the vendor in question has the ability to support those multi-band RF units within its 5G base station architecture, which they would surely claim to be able to. Ericsson too has recently proposed LTE/5G dynamically sharing spectrum in lower bands to support LTE-5G migration. At the time it said this was a unique feature, and it was also a popular demonstration on its MWC booth.

UPDATE – 29 March:

(I asked on Twitter for the thoughts of a few experts in this area and thought it might be interesting to collate them here. I would place a caveat that these are Twitter responses, given mostly on the spot, and we should treat them accordingly rather than as reflecting official positions of their companies. But taken on those terms they are of interest – Keith Dyer, Editor.)

As to whether Nokia has some sort of jump on other vendors, Gabriel Brown of Heavy Reading was of the view that others could mirror the solution in technical terms, if they wanted to. This was echoed by Andy Sutton of BT.

He added that such an overlay approach misses one of the prime benefits of deploying LTE and 5G NR where you can manage both layers together –  harnessing the ability to aggregate the LTE and 5G NR layers on the user plane, giving users a much faster connection.

Sutton said, “Any vendor could build 5G EN-DC [E-UTRA-NR Dual Connectivity] overlay, the advantage of doing this with existing 4G vendor is dual-connectivity option for the user plane. This offers significantly more spectrum to the aggregated 4G/ 5G UP [User Plane] than would be available with a simple 5MHz 4G control plane with NR UP.”

Ovum’s Daryl Schoolar had also spotted this drawback. He wrote, “I guess this wouldn’t allow for any data sharing on data plane between 5G & 4G for 5G users.”

Kye Prigg, until recently head of networks at Vodafone UK and now doing something similar for Rogers in Canada, was also on the case. His point appeared to be that you might risk moving from sort of one “lock-in” to another. That’s an interpretation, but here are his words: “Bit of a strange approach, sure it will get you to 5G if you are stuck with a vendor that for some reason you can’t use… Would be pushing the operator into a corner to swap the rest of the radios out over time including potentially any 2G and 3G to ensure spectrum re-purpose or dynamic sharing would be available in future.”

The frying pan/ fire situation was also touched on by technologist Dan Warren (it’s fair to point out here that although Warren has a senior role at Samsung Networks, he was responding in a personal capacity rather than providing any official response on behalf of his employer). Warren wrote, “The point in the article about closed X2 implementation is true. A solution from any vendor which is ‘buy a bit of our 4G with our 5G so we don’t have to open our X2 either’, isn’t actually a solution. It compounds the problem.”

This final point touches on one of the key reasons that some operators and vendors are looking into open radio access network designs in bodies like TIP and O-RAN Alliance. These would open up inter-layer interfaces, both within the RAN and in the overall network architecture to the core, and give operators more flexible deployment options.

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