[e2e] Simulator for wireless network

Detlef Bosau detlef.bosau at web.de
Sat Apr 21 11:12:10 PDT 2007

Glenn Judd wrote:
> We have been developing an approach that compliments the previously
> discussed options of simulation and experimentation: physical layer
> wireless emulation.

If I understand this correctly, you are ready to emulate the behaviour 
of a physical channel. Is this correct?

To my understanding, this is the by far most important part of the whole 
wireless network business. Many of the work in this area is, frankly 
spoken and I´m ready to take contradiction here, at least questionable 
because the assumptions about the lowest layers used in the system 
model, be it IP latencies or whatever, seem to be quite arbitrary and 
the question arises naturally whether they are chosen to "improve the 
results". Think of the whole work about spurious timeouts and the like. 
Some of this work even used a "Hiccup" module in the NS2, where 
arbitrary delay spikes were introduced in a flow. That way, I can prove 
anything or nothing. In this sense, an approach like this is,
I know I´m harsh here, worthless.

Of course, these results are artifacts.

And of course, when I do simulation my own, the results are artifacts.

The one researcher is lucky and gets it published, the other one gets it 
rejected. Neither way is sufficient.

The more I think about the whole wireless network business, the more I 
become convinced that it is absolutely inevitable to have good models 
and / or simulations and / or emulations of the wireless channel. All 
the rest is basically Garbage In Garbage Out.

Unfortunately, I´m not a communications engineer, so I´m absolutely not 
skilled enough to do this work on my own.
Otherwise, the criticism: "You miss a model of the wireless channel? So, 
start and build one!" would be perfectly legitimate.
Even more, I´m unemployed, so I don´t have the opportunity to make 
perhaps necessary physical experiments here.
I once was advised, I should try something with my mobile phone. Not 
only, this is by far too expensive, but when you make measurements on IP 
latencies, you have that many of unkown influences there, that it´s hard 
to get something useful from this.

I think, physical experiments should be done on an extremely low layer, 
e.g. with well known signal sources and mobiles which read these sources 
and measure the SNR or C/I and give you an insight of what´s happening 
on the "symbol layer". Upward from that, you can map this to block 
erasure rates or whatever you prefer. For your emulator, you perhaps 
won´t even map this because you emulate the physical channel

However, I think, what´s inevitable here is to have appropriate channel 
models, either analytical ones or replays from practical traces.

Question: What is the state of the art here? Are good channel models 

I think, this is the key question in this whole area.


Detlef Bosau
Galileistrasse 30
70565 Stuttgart
Mail: detlef.bosau at web.de
Web: http://www.detlef-bosau.de
Mobile: +49 172 681 9937

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