[e2e] Ressource fairness of PF scheduling and similar schemes in the presence of asymmetric fading.
detlef.bosau at web.de
Sun Nov 25 05:11:18 PST 2007
Once again me :-)
At the moment, I see two areas of interest in opportunistic scheduling
as it is used in HSDPA systems. (At least, they are of interest for me.
I don´t know the opinion of others people.)
For quite some time, proportional fair scheduling was state of the art.
Recently, some alternatives have been proposed.
The main shortcoming in PF scheduling is its behaviour in the presence
of asymmetric fading.
Thomas Bonald, "A Score-Based Opportunistic Schedulerfor Fading Radio
Intuitively, the reason for the problem is that SNR values for
different UEs may vary on different average values and with different
variation. Hence to compare SNR values for different UEs is often
comparing peaches and oranges.
To my knowledge, we have to approaches to overcome this problem.
One was developed within the Eurane Project, *
Fair Channel Quality-Based Scheduling Scheme for HSDPA System*
Al-Manthari, B.; Nasser, N.; Hassanein, H.
Computer Systems and Applications, 2006. IEEE International Conference on.
Volume , Issue , March 8, 2006 Page(s): 221 - 227
Digital Object Identifier
The idea is to use statistices "(SNR value - average) / standard
devation" instead of the original SNR values.
So, for any UE the considered statistics share a common expectation (0)
and a common variation (1) and are hence comparable.
Another approach is the aforementioned one by Thomas Bonald, who
basically (please correct me, if I have a misconception here) uses
quantiles / ranks as statistics to compare SNR values for different UEs.
In fact, quantiles are not mentioned explicitely in Bonald´s work, but
practically, this is the idea behind his approach: The actual SNR is
ranked within a set of n most recent SNR values.
Im not sure yet, whether we achieve comparable statistics here.
The other issue is ressource fairness / QoS in opportunistic scheduling.
I did some experiements with a token based approach during the last
weeks - however, the problem is to achieve stability because of the
uncomparable SNR statistics.
If we had SNR statistics which are i.i.d., a token based approach could
be helpful here, but I´m afraid that´s hardly to achieve.
So, at the moment, I plan to investigate some rate based approach.
The idea is to have some kind of "modified round roubin" scheduling, which
- enforces fair (or if QoS applies: according to contract) ressource
usage for any flow in the long run
- allows to use higher or lower ressource usage in the short run in
order to adapt the system to favourable or poor channel conditions.
I´m curious whether there are other people interested in this matter,
especially people from Germany.
Detlef Bosau Mail: detlef.bosau at web.de
Galileistrasse 30 Web: http://www.detlef-bosau.de
70565 Stuttgart Skype: detlef.bosau
Mobile: +49 172 681 9937
More information about the end2end-interest