What the [Bleep] Is Fronthaul?
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:
So, that's fronthaul, any questions?
— Dan Jones, Mobile Editor, Light Reading