[Ns-developers] spectrum modeling and wifi device

[Nicola Baldo]

Hi Ruben,

Ruben Merz wrote:
> So, you want to do two things in the wireless PHY of ns3: (1) support
> for multiple transmission channels at the PHY and (2) interference
> modeling at the receiver.

Our short-term goal is to simulate cognitive radio/dynamic spectrum 
access systems using the wifi MAC and the baseband part of the PHY. 
These systems are expected to operate in bands other than ISM, with 
different channel spacings. And we also want to evaluate the 
interference of this modified Wifi onto technologies other than Wifi 
(i.e., primary users). As a longer-term objective, we are also looking 
at possible ways to simulate OFDMA system, which need a rather complex 
spectrum modeling. Ideally, we would like to write a single piece of 
code which can be reused in all these cases. I think such a spectrum 
modeling feature could also be used for other scenarios, such as 
underwater communications.

Both the support for multiple channels in 802.11 and the modeling of 
adjacent channel interference are kind of a by-product of what we aim at.

Talking about performance, a detailed spectrum modeling would increase 
to some extent the computational load. That's why I liked the idea of 
allowing to plug below YansWifiPhy both the simple and fast 
YansWifiChannel, and a more detailed spectrum model for those who want it.



Ruben Merz wrote:
 >>> For interference modeling at the receiver, I think you don't have to
 >>> insert an object between YansWifiPhy and YansWifiChannel. What you
 >>> may want, is to get all the packets (irrespective of their
 >>> transmission channel) back to YansWifiPhy, and then process those 
 >>> packets in YansWifiPhy. Typically, you would do that at the same
 >>> time than you compute the SNR.
 >> Yes, this would be one way of doing this. You could also simply
 >> modelize this as an extra loss for incoming packets which is
 >> calculated based on the center frequency of the incoming packet and
 >> the center frequency of the receiver.
 >
 > Actually, it is complementary to the SNR calculation, right? But, yes,
 > the point of doing this is that it would allow you to properly model
 > cases where, for instance, transmission is deferred because of a
 > strong packet on an adjacent channel. You could also then properly
 > model the reception of a strong packet that is on an adjacent channel
 > than the receiver. Although I don't have any reference at hand, I seem
 > to remember that this can happen.

I like the idea of keeping the interference calculation in YansWifiPhy 
as-is, and just add the calculation of the loss due to use of different 
channels somewhere.

As for transmission deferral due to strong adjacent channel 
interference, wouldn't that be automatically handled by the 
"maybeCcaBusy" feature?


Regards,

Nicola