Light Reading

What the [Bleep] Is Fronthaul?

Dan Jones

Oh goody, another day, another new mobile industry buzzword to learn!

You might have seen the term "fronthaul" crop up in some of our stories recently. If you're like me, you may also have stopped and wondered: "Wait, what the f*** is fronthaul?" (See ADVA Adds Fronthaul for Mobile Versatility.)

As you might expect, it's a somewhat similar concept to backhaul, which, at its simplest, links the mobile network back to the wired network. In essence, fronthaul is the connection between a new network architecture of centralized baseband controllers and remote standalone radio heads at cell sites. (See LTE Base Station Challengers.)

Remote radio heads (RRHs) aren't some kind of robot band created because the real Radiohead got too lazy to tour. Rather, RRHs take the radio elements of a basestation and separate them from the baseband controller. This makes it easier to deploy the radios right at the top of a cell tower, eeking out a greater coverage range for the signal. (See AT&T: Why Our LTE Is Better.)

This separation, however, means that you need to connect the disparate radios to the centralized controllers via the standard Common Public Radio Interface (CPRI) in order to communicate. This also means that the point-to-point links need to be really fast in order to synchronize the transmissions across the network. Today, that means using point-to-point fiber links between the radios and the controllers, Heavy Reading senior analyst Gabriel Brown tells me.

"You can, in theory, do it over microwave [radio], but for now it's point-to-point fiber," he notes.

Essentially, fronthaul is one of the many elements that will make distributed LTE-Advanced networks -- a.k.a. Cloud-RAN (C-RAN) -- a reality, making 4G data faster and coverage more dense in the future. The need for point-to-point fiber links is an upfront capital expense for operators in the process of deploying these networks, but could deliver better networks, as Brown noted in a report last year: (See Why You Should Care About LTE-Advanced (Eventually) and C-RAN Blazes a Trail to True 4G.)

    The need for point-to-point fiber between remote radio units (RRUs) and baseband units (BBUs) is the Achilles' Heel of the C-RAN architecture. This is balanced by lower costs associated with other aspects of C-RAN, such as the ability to reduce cell site costs related to civil works, lease fees, power consumption and maintenance. Once fiber is in place, the C-RAN model becomes much more attractive. Perhaps for this reason, markets where operators are motivated to install fiber at scale, and where there is government encouragement for fiber deployment (e.g., China, South Korea, Japan, Singapore), the cloud RAN concept is more appealing in the nearer and medium term.

Here's a nice diagram to help you get it through your head:

From Remote Radio Head to C-RAN
(Source: Heavy Reading)
(Source: Heavy Reading)

So, that's fronthaul, any questions?

— Dan Jones, Mobile Editor, Light Reading

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User Rank: Light Sabre
11/12/2014 | 7:57:49 AM
Re: Fronthaul is a relative of DAS in a way
Hi Dan, you are totally right, in some scenarios it is really a competing technology, especially if you think that it is possible to do RAN Sharing. So you could share the RRH among different operators.

DAS and CPRI are being considered here in some scenarios for the Olympic games in 2016, where you cannot install so many telecom equipment in a same place.


DAS is better in some cases, CPRI is better in other cases.

User Rank: Blogger
2/24/2014 | 7:38:49 AM
Re: Fronthaul is a relative of DAS in a way
Thanks, just heard an operator talk about mobile networks of the future where the packet spends the least time in the air possible, so....
Jon B Transmode
Jon B Transmode,
User Rank: Light Beer
2/24/2014 | 6:52:26 AM
Re: Fronthaul is a relative of DAS in a way

Hi Dan, The first time I heard the phrase fronthaul I thought the speaker was making it up on the spot.

Fronthaul, and C-RAN in general, are interesting technologies and it will be interesting to see how they spread across the globe in the next few years. Some Asian operators are well down this path already and we've seen an uptick in interest in Europe and the Americas recently so it is certainly an area that many operators are looking into.

It is an area of networking that could be a great opportunity for optical networking vendors as operators move from the initial fronthaul over fibre to fronthaul over WDM. If they can support the tough latency and sync requirements that the CPRI and OBSAI standards require. Of course, fibre availability will be a key requirement and perhaps a limiting factor in some locations.

As an industry move that has largely been driven by the wireless operators rather than vendors it has some real traction behind it. The whole C-RAN business case (consolidated BBU clusters to support current and future wireless network architecture trends and lower power costs and space in cell sites) is the main driver for fronthaul as you mentioned in your piece. So fronthaul plays an important supporting role to C-RAN that can make or break the overall C-RAN business case.

Anyhow, interesting times!
User Rank: Blogger
2/24/2014 | 3:36:54 AM
Re: Fronthaul is a relative of DAS in a way
Yes, I would say so.
User Rank: Light Sabre
2/23/2014 | 2:24:46 PM
Re: Fronthaul is a relative of DAS in a way
That's what I was guessing about too. With the tremendous surge in mobile device useage, what's going to be the best technical while still economic solutuion to handling all the new traffic at speeds customers want or need?
User Rank: Light Sabre
2/22/2014 | 9:47:52 PM
Re: Fronthaul is a relative of DAS in a way
It sounds like fronthaul is going to be needed in some of the most densely packed urban areas in order to deliver the amount of data people require. There is only so much physical space in these areas.

Would this be the most important application for this?
User Rank: Blogger
2/21/2014 | 9:40:55 PM
Re: Fronthaul is a relative of DAS in a way
I'm certainly over it!
Liz Greenberg
Liz Greenberg,
User Rank: Light Sabre
2/21/2014 | 9:36:05 PM
Re: Fronthaul is a relative of DAS in a way
So fronthaul added to backhaul equals overhaul?  I think that I get the picture...DAS the point right?
User Rank: Blogger
2/21/2014 | 4:40:56 PM
Fronthaul is a relative of DAS in a way
Fronthaul is not dissimiliar to DAS in concept. The difference being that traditional distributed antenna systems share bandwidth whereas using the point-to-point fiber links gets each RRH a really fast connection.
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