Today we’re discussing a relatively old, yet new, subject which still creates industry debates on its applicability for the majority of the world’s networks. What I would like to do before we dive into the fronthaul definitions, is to take a step back and discuss the relevant alternatives for increasing capacity coverage in a modern mobile network and its impact on operations, access spectrum utilization and the back or front haul – or in short – hauling segment. Obviously, the main industry discussion is around small cells. When we’re talking about a small cell environment we should expect to have the following four main types which will likely coexist together in the network in the near future:
The Offload Model – Either WiFi or femto based, running off net on any broadband connection connected to a gateway somewhere in the network where it joins back to the mobile network
The Integrated Model – The integrated model is just as a regular small cell that everybody is referring to. Basically a macro-cell functionality, but with lower power. It’s a relatively low cost device. It’s not really tiny but it also comes with all the requirements from an LTE-eNodeB. Meaning all the requirements in timing (1588 etc), capacity (>100 Mbps) and latency (<10 Msec e-t-e) are there.
The Coordinated Model – Coordinated is something that does not exist today. It will arrive in a year or two with arrival of LTE-Advanced (3GPP rel 10 and 11). With, eICIC – Enhanced inter cell interface cancellation, Base stations have higher requirements. And when we talk about higher requirements it’s higher requirements in capacity and in latency. As these eNodeBs need to coordinate in real time with their peers we will need to target 1-5 m/sec instead of 10msec. The desired benefit to operators is to only use three Coordinated small cells for every macro compared to ten regular small cells expected ratio and still achieve the same capacity coverage targets.
The Distributed Model – Distributed macro cells takes small cells to a whole different level. Instead of deploying those independent small cells, operators can drop radio units or micro/Pico radio units.
The basic idea is to deploy more sectors – instead of three or six, why not 20? Much of that will be for indoor coverage but will also function for outdoor use. The savings can be found in real estate used and truck rolls as radio units are simpler and smaller when compared to the costs of running a complete base station. The way we connect base band units or as we call them, digital units (DU) with the remote radio head or unit (RU) using a carrying Common Public Radio Interface (CPRI). Originally planned to carry traffic between the base of the tower and the top over fiber for a very short distance, it is easy to see you can extend the distance to few miles easily either using available fiber assets or high capacity wireless solutions.
This connectivity is called fronthaul and we will dedicate more time trying to understand the relation with C-RAN and weigh the alternatives.