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I don’t know how many of you know but for the last 2 years I have been pretty focused on small cell deployment, indoors and outdoors, as well as Macro deployment. The HetNet deployments are going to start next year. I see the upgrades on the existing tower as well as deployment of the stand alone sites, mostly small cells but some higher power, 10 to 20 watts, cell sites for “densification” of LTE systems to help offload Macro sites. So let’s talk about that.
All the small cell names can be confusing. It adds a great deal of confusion to the deployment teams as well as some of the carriers.
I worked on some AT&T Wireless and Verizon Wireless offers where they were very careful to use the proper names for the proper small cell. They made sure that a Femto Cell was used for home use and that a Metro Cell is used for outdoor areas and the Pico Cell was used for small to midsized businesses.
Of course I dealt with a few other carriers that just called them all small cells or pico cells, no differentiation at all.
I thought I thought it might be a good idea to put this chart together to help you out. Eventually they will all be indoor or outdoor small cells, but until then let’s look at the naming nomenclature. This will also cover some usage applications.
Small Cell: First off, there is the small cell where the unit has everything, except maybe the router, but the BBU, (broadband unit) and the Radio Head are all in one unit. These are very common now. Generally small cells are under 5 watts. Many times if they are indoors they are 1 watt or less. Similar to Wi-Fi but on a licensed band.
Femto Cell: This is usually the private small cell. It may be something that a person would put in their home or a small business to improve coverage. Small loading and usually just for a few connections. Most of the time it just connects to the internet, like someone’s cable modem.
Pico Cell: This is slightly bigger than the Femto, usually for a mid-sized business, bus station, or a smaller stadium to connect maybe 10 to 100 connections at any given time. Possibly more, depending on the application.
Micro Cell: This is usually a bigger unit that can handle larger stadiums or a train station or airport. This term is not used so much anymore because they just call it a small cell.
Metro Cell: This term was used for larger outdoor metro areas where the loading could be greater than 100 users at any given time. But let’s face it, they are commonly called small cells.
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Indoor small cell: Just like it says, it is a small cell that is mounted inside a building. It could be the small cell or a RRH that is mounted somewhere it is needed. In today’s world it is about coverage and loading. Loading is very important in the LTE systems.
Outdoor Small Cell: It is a small cell mounted outdoors, same reason, to help with coverage and loading.
Distributed radio system: Then there is the RRH, (Remote Radio Head), that’s part of a distributed radio system. The RRH could be at the top of the tower, other parts of a building, or a few miles away mounted on a light pole. The BBU may be located on a different location than the RRH. This is pretty common in today’s world. You know that on the towers they put the BBU on the ground and the 
RRH is up on the tower with the antenna. So just imagine now that they put the BBU in a basement and the RRH’s are spread throughout the building. They may also have the BBU in a closet at a building and spread the RRH’s all over town to get the RF where the people are, to distribute the radio heads and antennas. This could be part of a DAS system where they rely on the CPRI, (common public radio interface), to be connected to fiber for the “front haul” which is like the backhaul but to go from the BBU to the RRH, forward! Currently there are several limitations which mostly have to do with timing. They can only travel so far before they would time out. That limits distance at this time. The cloud may change that soon. When they locate many BBUs in a remote location for widely distributed RRHs, they call that a BBU hotel, a term that means that many BBUs for multiple locations are in one spot. I believe that with the cloud this may change because BBUs will be located farther and farther away.
DSCS: Distributed Small Cell System is where you would deploy small cells, (and maybe Wi-Fi) like you would with a DAS system. These would be stand alone all-inclusive small cells with integrated antennas. They would be connected with fiber or CAT5 or some type of wireless backhaul.
So as you can see small cells serve as a solution in many cases and there were many names for them. Today most people just say small cell for everything except the Femto. The Femto is a specific use small cell.
I did not bring up DAS too much because it is something that could be a separate solution or this could be part of a DAS solution.
I would think that when CRAN takes off and is common then all you will need is a decent backhaul connection to connect anywhere. And there it is, backhaul, one of the major deployment problems with small cell. Sprint is trying to drive down the price of backhaul so they can reasonable deploy CRAN and small cells everywhere. Also because they probably don’t sell backhaul anymore!
Speaking of backhaul, another solution that could be rendered is a UE relay. (UE is User Equipment like your smart phone.) A way to use a carrier’s bandwidth to provide backhaul to a MACRO site. Think of it working like one of those devices that provide Wi-Fi using the carrier for the connection. I think it is a great idea, if you have spare bandwidth. I was hoping the FCC would push through the light licensed 3.5GHz band with more bandwidth; remember the citizen’s broadband radio service? We could use that for backhaul, if there is enough bandwidth, then we could see small cells in that band to be utilized for backhaul for other small cells. That’s my dream to see one system support the many other systems in this ecosystem. Sign me up to build that out, a backbone system of fixed wireless to support the mobile wireless systems. Just a thought about how to affordably extend the last mile without using the precious bands that the carriers paid so much for.
Interested? Let me know about it. I will add you to my email list for more information.
Be smart, be safe, and pay attention!
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