How we tested the dependence of LTE speed on S1 parameters

It was a year ago. Start of LTE launch in our Macro Region. At the same time, the radio of one Korean vendor is very rare, even on a global scale (no, the BS is not on Android - I checked it). It seems that everything has been taken into account, tests have been carried out in the laboratory, schemes have been developed, typical configurations. Well, as usual, run. The launch is not with us, but in the neighboring region.

It seems to be close, but somehow the results are not encouraging - the subscriber speed is lower than the laboratory one in the same radio conditions. And soon the launch of the network - you need to show the maximum, and not as competitors .

What to do? Joyfully troubleshit!



In fact, troubleshooting did not take much time and the reason was quickly found - the highway. The quite good backbone for 2G and 3G turned out to be "so-so" for LTE. Transferred to the reserve - the problem is gone.

But the question arose - what do we need? What channel quality is required? 113 orders are executed with a large margin, internal standards, too, but they are clearly not enough. Well, let's try to understand what is needed. We quickly assemble the laboratory, but only against the S1 interface between the base station (BS) and the transport network, we put a small helper in the form of a server with Debian on board. Settings are searched surprisingly quickly and by the end of the day the lab is ready.

The scheme is very simple (the dotted line shows the traffic path):



* MBH - mobile backhaul - transport network.
* EPC - evolved packet core - packet core.

Yes, why did you need a server contrary? Make losses and delays. Oddly enough, this turned out to be the easiest solution to simulating problems. Tcand nothing more is needed. Server latency is minimal.

The subscriber speed was measured quite honestly - a “whistle” on a laptop and an ftp server on the Internet. I will run ahead and say that the sample was more or less honest - each of the possible options was measured 10 times. The best and worst were discarded; the rest was averaged. However, errors are possible due to imperfect monitoring tools on the subscriber unit. Although experience has shown that specialized complexes may also have problems with accuracy.

And one more refinement for ease of understanding the following results: 1 stream / 4 stream is the number of download streams. Those. either 1 or 4 files at a time. The speed for 4 files is of course total. And yes, speedtest is a few threads, so the 4-thread option is much closer to reality.

So, what happened:

1. Average speed:



2. Maximum speed:



Delay certainly affects, but it is very difficult to minimize. And the main problems are still due to drops. Ministerial 10-3 look very sad. It became obvious that our goal was at least an order of magnitude higher and a set of measures was taken to achieve it. And 10 -5 already allows you to reach a maximum under almost any conditions. That's just to reach 10 -5 does not always work, but that's another story ...

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