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What is LTE UE backhaul? It is backhaul that uses the carrier’s spectrum, just like the UE, User Equipment, you smartphone. If you have ever used a carrier’s Wi-Fi hotspot then chances are you have used a device similar to this. One that will use the carrier’s spectrum, like LTE, for backhaul. This is something that is commonly used for internet access when there is no Wi-Fi available. The carriers all sell these units and many of today’s smartphones do something similar. However, they just use the standard signal. Using it for a tiny hotspot and for an eNodeB are 2 different things.
Let’s talk hotspot. Many vendors provide equipment that a user can add coverage quickly and easily. A quick Wi-Fi connection to the internet using the carrier’s LTE. Everyone has Wi-Fi and there are devices that create an instant hotspot. Verizon has the Mi-Fi or you can use your smart phone as a hotspot. Every carrier has a wireless modem that you will provide a Wi-Fi hotspot. I think anyone reading this probably knows about the hotspots. I thought it would be a good example to get started.
I am bringing this up because now there is talk about using the UE backhaul for small cells making it a more powerful cell extender. It sounds like a great idea on the surface. This is a cheap, quick and easy backhaul. However, what are the drawbacks?
What is a cell extender? There is a practice where many carriers will use a cell extender that will have a UE relay backhaul to extend the signal. This is also like a smartphone hotspot or a Mi-Fi unit because it was just to help a few customers but extends the carriers signal instead of Wi-Fi. This is a type of repeater to extend the macro’s signal, a cell extender. This is a way for the carrier to extend the coverage just a little bit farther. It’s a way to provide coverage someplace quickly and easily. These were common in 2G, 3G, and now LTE. It is a simple and quick way to install a repeater to extend carrier coverage down an ally. In the old days of DAS, this is really what they did. They would take the signal where it was strong or use an antenna and amplifier to increase the strength to get it into a dead spot. People paid a lot of money for these systems.
What about using UE backhaul for an eNodeB? You know, like a small cell or a mini macro? I am bringing this up because now there is talk about using the UE backhaul for small cells making it a more powerful cell extender. It sounds like a great idea on the surface. This is a cheap, quick and easy backhaul. However, what are the drawbacks?
It’s not a simple cell extender, and let me tell you why. Now you are talking about putting the small cell in an area where there is a loading issue. This goes beyond coverage. The data and spectrum usage could go through the roof! So if you set it up like a cell extender with backhaul to the macro site, then guess what! You will see an overloaded macro sector! The macro not only has to deal with all of its users but all the small cell or Mini macro users too. This sucks up all the spectrum and bandwidth for that sector. What can be done? Read on!
To break the bottleneck you need to dedicate spectrum in the macro eNodeB that will be feeding the UE backhaul. This will alleviate the spectrum usage for the regular users on the macro sector. We don’t want them to get knocked off if the small cell US backhaul overloads the macro. This will make it so that the users on the macro don’t get shut knocked off if the small cell pulls the entire spectrum for its users. This will allow the small cell UE backhaul to have a dedicated pipe. It needs to have dedicated spectrum for this purpose. Then the small cell will know how much backhaul spectrum it has to available. By the way, not an easy change, changes in the eNodeB and possibly the core need to be considered as well as neighboring sites. This “dedicated backhaul spectrum” needs to be set aside in this sector and others too. It takes some planning and changes.
You could still have the data bottleneck at the macro’s backhaul. That’s another issue that needs planning.
So now you dedicated part of the band to the UE backhaul, which seems OK. Remember that the carrier paid a lot of money for that spectrum and now they are choosing to use it for backhaul. So the pipe is limited based on coverage and availability. It is a quick and easy to add UE backhaul, but is this the best use of the spectrum? Will you lose something in this backhaul? Yes, you have delay issues, timing issues, and neighbor issues. All of this is a problem when building a site for any type of real loading. Go to the links below to learn more.
However, what’s the real issue? Is it all the problems I mentioned above? They are all technical issues that good engineers will resolve. This appears to be a cheap and quick solution. But that’s not the real issue, is it? The carriers paid a crap ton of money for spectrum. Is backhaul a smart way to use this resource? Is that billion dollar investment there to save some CapEx for the company? I thought it was for the customers! Backhaul could have been something in the unlicensed band for a lot less money. It could be a fiber link for more money. Is this an easy out or will it cause problems down the road because the spectrum is only going to get more and more valuable? Do investors want to see that spectrum used this way? I don’t see the auctions being a cheap alternative to providing backhaul.
So just because it looks cheap and easy doesn’t mean it’s a good move strategically. Don’t get me wrong, the UE relays, the repeaters serve an important purpose for coverage and filling holes, I am just saying be strategic and think it through. For more information hit the links below to learn about these solutions.
http://lteworld.org/blog/introduction-relay-nodes-lte-advanced
http://wireless.skku.edu/english/UserFiles/File/1569472705.pdf
http://www.ericsson.com/res/docs/2013/lte-in-band-relay-prototype-and-field-measurement.pdf
http://www.airspan.com/products/airvelocity-2/
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