[mab-wifi] Possible contribution

[Toke Høiland-Jørgensen]

Pasquale Imputato <p.imputato at gmail.com> writes:

> Hi Toke,
>
> sorry for the long delay.
>
> In ns-3 the 802.11 standard is implemented rather accurately.
> The simulator models the standards 802.11a/b/g/n/ac, an initial draft of ax and the e emendament for the QoS support.
> The models support MIMO in 802.11n/ac/ax. 
> The example 802-11n-mimo in examples/wireless provide and overview of the MCS and MIMO capabilities by exploring for each HT MCS from 1 to 4 MIMO streams.
>
> Multiple rate control algorithms are implemented in the simulator. Some of them are found on real devices, while much others are only available in literature. There is implemented the minstreal HT algorithm, that could be useful for benchmark.
> The rate control algorithms are modelled by the WiFiRemoteStationManager class of the wifi module. The class hold a list of per-station-state info modelled after the struct sta_info in Linux kernel. 
> Create a new rate control algorithm can be done by introducing a new child class of the WiFiRemoteStationManager class in the wifi module of the simulator.
>
> The simulator capabilities seem to fit our needs in term of MCS and
> MIMO.

Yeah, this sounds great! Looking at the WiFiRemoteStationManager code,
there's an "IsLowLatency" property which indicates that the model can
make decisions for every packet. If this is *not* set, how does a model
then make decisions? And is there a concept "retry chains" for the rate
selection algorithm (where a sequence of rates to try are picked at once
when a decision is made)?

> Since we are in an exploration phase, how we can contribute to the
> exploration?

I think the two main things we are trying to figure out are the
correlations between different rates. Which involves answering
questions like:

1. What correlations exist between the success probabilities of sending
   at different rates. I.e., can we always assume that if a transmission
   fails at a low rate (more robust encoding), it would also have
   failed at a higher rate (or conversely, if it succeeds at a high
   rate, it would also have succeeded at the lower rate). Does this hold
   within the same MIMO configuration? What about between different MIMO
   configurations?
   
2. How does rate influence collision probability in the presence of
   several nodes? I.e., if we send the same transmission size at a lower
   rate, it is going to take longer to send; does this affect the
   probability of collision with other nodes? If it does, how pronounced
   is this effect?

3. How does transmission (aggregation) size affect the success
   probability of transmitting at a certain rate?


Another thing that could be useful is producing some test data sets (of
"ground truth") that we can use for evaluating algorithms on. For
instance, given a static scenario of N clients connected to an access
point, produce a data set which contains the steady state success
probabilities for each rate (for each node). And another data set which
introduces mobility (at a credible rate) and makes the rates a function
of time.

Does any of the above sound doable? :)

-Toke