[Ns-developers] wireless PHY project

[annalisa]

Thanks for your reply.
But, if take a look at the formula of the Shadowing, for example in the
Rappaport's book, you can find that
the received power is a random variable. But there is not any dependence on
time!
The shadowing accounts for the different distribution of clutter around the
devices.
The temporal variation are in general due to the fast fading, that is what
you pointed out by the example of the laptop. There are some distribution
for the fast fading, like Ricean, and this is a very good starting point.
Another point to strength the definition of shadowing is that it is usually
used to compute the coverage of a cell.
The power it computes is the MEAN value!
Regards
Giuseppe


Anders L Nilsson wrote:
> 
> Hi all,
> 
> I had a look at the wireless PHY wiki again:
> http://www.nsnam.org/wiki/index.php/Ns3WirelessPhy
> 
> I have a problem with the following section: "Be aware that the
> current Shadowing
> model implemented in ns-2.xx implements a Shadowing model which is
> time-varying,
>  i.e. at every signal(packet9 reception the Shadowing formula is
> applied. This means
> that every packet will see different path loss. This is not true. In
> reality, the shadowing is static. After generating the path losses,
> they should be constant during the simulation."
> 
> Actually, in reality, shadowing is never constant. Even when the two
> communicating nodes are stationary, the environment is constantly
> changing, cars are moving, people are walking by, trees are waving,
> windows and doors opens and closes etc. Path loss and shadowing are
> not the same thing. Maybe if you are somewhere out in deep
> interstellar space, you will see no shadowing. But I believe at least
> 90% of the users of NS3 will want to simulate at least a semi-urban
> environment.
> As a simple test you could turn on your laptop, connect it to an
> access point, sit still and monitor the rx signal strength, and you
> will see that it varies a few dB even if you are not moving an inch.
> 
> So what I am saying is that the path loss do vary with every packet
> reception, and this variation should be a configurable parameter
> depending on the type of (urban) environment you are simulating.
> 
> regards,
> Anders
> 
> On 11/15/06, annalisa <demarco at fit.ac.jp> wrote:
>>
>> Have you ever used this package?
>>
>> http://www.comp.nus.edu.sg/~wuxiucha/research/reactive/release/wireless_transmission_error.tar.gz
>>
>> It seems to include most of our dilemma about interference and fading
>> modelling.
>> I took a look at the code, and I' am not sure if the implementor decrease
>> the interfence
>> amount one the interering packet ceases transmission.
>> However, in ns-3 have these solutions been implemented?
>> Regards
>> Giuseppe De Marco
>> FIT, JAPAN
>>
>>
>> Mathieu Lacage wrote:
>> >
>> > Hi all,
>> >
>> > The ns-3 project is the opportunity a lot of people had been waiting
>> for
>> > to get world-class wireless simulation support. This support will
>> depend
>> > largely on the PHY-level layer provided by ns-3. As such, I would like
>> > to start the "ns-3 wireless PHY" project whose aim is to build a set of
>> > PHY-level models for wireless mediums able to accomodate the needs of a
>> > broad spectrum of users:
>> >   - 802.11a/b/g
>> >   - bluetooth
>> >   - GSM/UMTS/EDGE/GPRS
>> >   - satellite
>> >   - wimax
>> >   - your favorite wireless system
>> >
>> > It is quite obvious that no single model will be able to catch
>> > accurately the characteristics of each of these transmission system
>> > which is why I think it is important we provide a set of different
>> > models and a single interface to access all these models to be able to
>> > switch easily from one model to the other, thus allowing model
>> > comparison.
>> >
>> > Because I have a little bit of experience with 802.11 PHY models, I
>> have
>> > started adding content to the following wiki page
>> > (http://www.nsnam.org/wiki/index.php/Ns3WirelessPhy). It would be
>> > awesome if others could start to do any of:
>> >   - add descriptions of other wireless systems they would like to
>> > modelize
>> >   - add descriptions of models they would like to add
>> >   - start discussions on the ns-developers mailing-list
>> >
>> > Idealy, the outcome of this project would be:
>> >   1) a single interface to send and receive packets but also to sense
>> > the status of the wireless medium
>> >   2) multiple implementations of this interface
>> >   3) documentation detailing the model behind each implementation
>> >   4) documentation detailing "current best practice": when and where
>> the
>> > models should be used
>> >
>> > So far, I think that we should focus on 3) and 4): implementations
>> > should not be too hard to come up with once we have gathered enough
>> > requirements and model descriptions.
>> >
>> > Mathieu
>> >
>> >
>> >
>>
>> --
>> View this message in context:
>> http://www.nabble.com/wireless-PHY-project-tf2502315.html#a7352145
>> Sent from the ns-developers mailing list archive at Nabble.com.
>>
>>
> 
> 

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