[e2e] Simulator for wireless network
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.
Mail: detlef.bosau at web.de
Mobile: +49 172 681 9937
More information about the end2end-interest