[LENA] Question about fading model

[Xing Xu]

Dear all,

I've played with NS3 LTE module a lot, but I'm new in LTE area. I have a question about fading model. Clearly I can enable the fading (using one given trace), and it provides me signal variation (and thus throughput variation).

However, from the manual, I don't know how does this fading implemented (is it delta on each CQI)? What is contained in the fading trace (deltas)? and how should I use it (say, I have different scenarios, should I use the same trace)?

Now, what confused me is that, if I'm using the same fading trace, it hurts the throughput much more when the channel condition is bad compared to when channel condition is good (e.g., when the UE is close to the base station, there is variation due to fading but not much, but when the UE is faraway, e.g., close to the edge between two base stations, the throughput is really degraded, however, without fading the throughput can be good). So I wonder whether I've used the fading trace in the wrong way, like, I should generate and use a different fading trace when my UE is faraway.

I hope some one can explain how does fading trace work at a high level to me...

Thanks,

Xing

[Marco Miozzo]

Hi,

the fading traces are matrices of the value of fading that is used by channel model to evaluate the pathloss, therefore they affect directly the SINR.

When UE is closed the signal is high therefore the effect of fading is lower.

So the behavior you are experiencing is the correct one.

Best,

marco.

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[Xing Xu]

Thanks, Marco. I don't quite understand the part that "when UE is closed the signal is high therefore the effect of fading is lower." Can you explain more (or point me to a reference)?

So fading traces are "deltas" for pathloss, and thus it affect the "Signal" part of SINR, right (signal = tx power - pathloss)? I'm trying to understand what does this "delta" mean and how should I use these "deltas". For example, if one delta is, e.g., 5dB, then when I'm using the fading trace, this 5dB adds to my pathloss directly, no matter what is the pathloss value (that means, if my pathloss is 100dB, I add 5dB; if it's 10dB, I still add 5dB), or what?

I guess I'm missing the piece about how to correctly apply those fadings: these fadings are generated in one scenario, how can we apply those changes to a completely different scenario?

[Marco Miozzo]

your example on the impact is correct.

In case you want to generate different traces you can generate new ones with the MatLab simulation script, more info at the following link:

http://lena.cttc.es/manual/lte-user.html#fading-trace-usage

best,

marco.