LTE Network Design Advice: Don’t Overlook the X2

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This should be quick…Often times I am asked what can be done to improve network performance. There are all of the obvious answers such as those related to the radio link and the backhaul so on but the one I see as the most underrated improvement time after time is the X2 interface.

The S1 interface connects the eNB to the Core network. That is not what I’m talking about.

The X2 interface was designed to directly communicate from site to site, to reduce the latency of handover between sites with control and user plane data and allow for the exchange of control information that is useful to Self Organizing Networking (SON).

An LTE Network Diagram

An LTE Network Diagram

Seems like everyone I visit has connected their X2 interface (a logical interface) just back through the same path as their S1 interface. What’s the point of that? course_024_dWhen it takes the same path as the S1 (from site to edge router to core and back.)I mean all that latency those packets rack up on that trip!

The push back I hear time after time is that X2 is marginally useful and after some questions, hand wringing and argumentative push back, they rationalize that if they were to theoretically build it as a separate network, it would just add a lot of cost and aggravation with very low benefit.

I beg to differ.

If you were to build a dedicated direct path X2 network, from each site to it’s neighbors, there are many many areas of performance gain. Fewer drops, faster hand over, more relevant communication exchange about state between sites (better SON), better CoMP (Coordinated Multi Point), a little backhaul offload and so on and so on. Found this picture from Cambridge Networks (that they re-used from Qualcomm) that summarized 1 benefit nicely..



So there are obviously some constraints such as if you are building a 700MHz network in a rural area and the cells are very large then the benefits are reduced a bit… In most cases the benefits are straightforward. To do this you need to determine a good way to interconnect the neighboring eNBs for max economic benefit. There are ways of doing this. Point to point, point to multipoint etc etc…

One of the more effective and exciting ways to me is having intermediate connections as small cells! Kills the edge performance/indoor issues and can be leveraged into compelling intermediary sites to allow a more ‘free spectrum’ technology approach to connecting the X2.

X2, try it. You will like it.

hqdefault(This is Mikey that used to be on Life Cereal commercials..
young people won’t get the reference…. But he tried it, finally…